[PATCH] replace SYSV shared memory with shm filesystem

[PATCH] replace SYSV shared memory with shm filesystem

[Christoph Rohland]

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Hi folks,

This patch implements a minimal filesystem for shared memory. It
replaces/reuses the existing SYSV shm code so you now have to mount
the fs to be able to use SYSV SHM. But in turn we now have everything
in place to implement posix shm. This also obsoletes vm_private_data
in vm_area_struct.

Also it is now possible to do e.g. 'rm /dev/shm/*' instead of this
terrible 'ipcrm shm xx' :-)

You can mount the fs only once. This will probably break shm in
chrooted environments.

It is heavily tested from UP to 8way SMP with HIGHMEM. On the latter
the shm handling triggers some mm bugs under heavy swapping. But these
problems also exists in the stock 2.3.36 kernel (I cannot boot
2.3.3[78] on my 8way). I will report these problems later in a
separate mail.

Greetings
		Christoph


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diff -uNr 2.3.38/Documentation/Changes c38/Documentation/Changes
--- 2.3.38/Documentation/Changes	Sun Jan  9 11:44:36 2000
+++ c38/Documentation/Changes	Sun Jan  9 19:04:43 2000
@@ -72,6 +72,9 @@
 General Information
 ===================
 
+   To use System V shared memory, you have to mount the shm filesystem
+somewhere.
+
    <CTRL><ALT><DEL> now performs a cold reboot instead of a warm reboot
 for increased hardware compatibility.  If you want a warm reboot and
 know it works on your hardware, add a "reboot=warm" command line option
diff -uNr 2.3.38/fs/exec.c c38/fs/exec.c
--- 2.3.38/fs/exec.c	Thu Jan  6 14:05:53 2000
+++ c38/fs/exec.c	Sun Jan  9 11:47:23 2000
@@ -322,7 +322,6 @@
 		mpnt->vm_ops = NULL;
 		mpnt->vm_pgoff = 0;
 		mpnt->vm_file = NULL;
-		mpnt->vm_private_data = (void *) 0;
 		vmlist_modify_lock(current->mm);
 		insert_vm_struct(current->mm, mpnt);
 		vmlist_modify_unlock(current->mm);
diff -uNr 2.3.38/fs/namei.c c38/fs/namei.c
--- 2.3.38/fs/namei.c	Thu Jan  6 14:05:53 2000
+++ c38/fs/namei.c	Sun Jan  9 11:47:23 2000
@@ -991,7 +991,7 @@
 	return error;
 }
 
-static inline int do_unlink(const char * name)
+int do_unlink(const char * name)
 {
 	int error;
 	struct dentry *dir;
diff -uNr 2.3.38/include/linux/fs.h c38/include/linux/fs.h
--- 2.3.38/include/linux/fs.h	Sun Jan  9 11:44:41 2000
+++ c38/include/linux/fs.h	Sun Jan  9 11:49:33 2000
@@ -865,6 +865,7 @@
 extern struct dentry * open_namei(const char *, int, int);
 extern struct dentry * do_mknod(const char *, int, dev_t);
 extern int do_pipe(int *);
+extern int do_unlink(const char * name);
 
 /* fs/dcache.c -- generic fs support functions */
 extern int is_subdir(struct dentry *, struct dentry *);
diff -uNr 2.3.38/include/linux/mm.h c38/include/linux/mm.h
--- 2.3.38/include/linux/mm.h	Sun Jan  9 11:44:41 2000
+++ c38/include/linux/mm.h	Sun Jan  9 11:49:33 2000
@@ -60,7 +60,6 @@
 	struct vm_operations_struct * vm_ops;
 	unsigned long vm_pgoff;		/* offset in PAGE_SIZE units, *not* PAGE_CACHE_SIZE */
 	struct file * vm_file;
-	void * vm_private_data;		/* was vm_pte (shared mem) */
 };
 
 /*
diff -uNr 2.3.38/ipc/shm.c c38/ipc/shm.c
--- 2.3.38/ipc/shm.c	Sun Jan  9 11:44:41 2000
+++ c38/ipc/shm.c	Sun Jan  9 19:33:55 2000
@@ -9,8 +9,18 @@
  * BIGMEM support, Andrea Arcangeli <andrea@suse.de>
  * SMP thread shm, Jean-Luc Boyard <jean-luc.boyard@siemens.fr>
  * HIGHMEM support, Ingo Molnar <mingo@redhat.com>
- * avoid vmalloc and make shmmax, shmall, shmmni sysctl'able,
- *                         Christoph Rohland <hans-christoph.rohland@sap.com>
+ * avoid vmalloc, make it a file system
+ * 			Christoph Rohland <hans-christoph.rohland@sap.com>
+ *
+ * The filesystem has the following restrictions/bugs:
+ * 1) It only can handle one directory.
+ * 2) Because the directory is represented by the SYSV shm array it
+ *    can only be mounted one time.
+ * 3) This again leads to SYSV shm not working properly in a chrooted
+ *    environment: If the mount point exists under the chroot it will
+ *    create regular files there. If it doesn't, shmget will fail.
+ * 4) Read and write are not implemented (should they?)
+ * 5) No special nodes are supported
  */
 
 #include <linux/config.h>
@@ -19,6 +29,9 @@
 #include <linux/swap.h>
 #include <linux/smp_lock.h>
 #include <linux/init.h>
+#include <linux/locks.h>
+#include <linux/file.h>
+#include <linux/mman.h>
 #include <linux/vmalloc.h>
 #include <linux/pagemap.h>
 #include <linux/proc_fs.h>
@@ -29,14 +42,31 @@
 
 #include "util.h"
 
+static struct super_block *shm_read_super(struct super_block *,void *, int);
+static void	      shm_put_super  (struct super_block *);
+static void	      shm_read_inode (struct inode *);
+static void	      shm_write_inode(struct inode *);
+static int	      shm_statfs (struct super_block *, struct statfs *, int);
+static int	      shm_create   (struct inode *,struct dentry *,int);
+static struct dentry *shm_lookup   (struct inode *,struct dentry *);
+static int	      shm_unlink   (struct inode *,struct dentry *);
+static int	      shm_notify   (struct dentry *dent, struct iattr *attr);
+static void	      shm_delete   (struct inode *);
+static int	      shm_mmap	   (struct file *, struct vm_area_struct *);
+static int	      shm_readdir  (struct file *, void *, filldir_t);
+
+static char *ipc_path;
+#define SHM_NAME_LEN NAME_MAX
+#define SHM_FMT ".IPC_%08x"
+#define SHM_FMT_LEN 13
+
 struct shmid_kernel /* extend struct shmis_ds with private fields */
 {	
 	struct shmid_ds		u;
 	unsigned long		shm_npages; /* size of segment (pages) */
-	pte_t			**shm_dir;  /* ptr to array of ptrs to frames -> SHMMAX */ 
-	struct vm_area_struct	*attaches;  /* descriptors for attaches */
-	int                     id; /* backreference to id for shm_close */
-	struct semaphore sem;
+	pte_t			**shm_dir;  /* ptr to array of ptrs to frames */ 
+	int			namelen;
+	char			name[0];
 };
 
 static struct ipc_ids shm_ids;
@@ -52,9 +82,7 @@
 #define shm_buildid(id, seq) \
 	ipc_buildid(&shm_ids, id, seq)
 
-static int newseg (key_t key, int shmflg, size_t size);
-static int shm_map (struct vm_area_struct *shmd);
-static void killseg (int shmid);
+static int newseg (key_t key, const char *name, int namelen, int shmflg, size_t size);
 static void shm_open (struct vm_area_struct *shmd);
 static void shm_close (struct vm_area_struct *shmd);
 static struct page * shm_nopage(struct vm_area_struct *, unsigned long, int);
@@ -63,6 +91,67 @@
 static int sysvipc_shm_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data);
 #endif
 
+static struct super_block * shm_sb;
+
+static struct file_system_type shm_fs_type = {
+	"shm",
+	0,
+	shm_read_super,
+	NULL
+};
+
+static struct super_operations shm_sops = {
+	shm_read_inode,		/* read_inode */
+	shm_write_inode,	/* write_inode */
+	NULL,			/* put_inode */
+	shm_delete,		/* delete_inode */
+	shm_notify,		/* notify_change */
+	shm_put_super,		/* put_super */
+	NULL,		 	/* write_super */
+	shm_statfs,		/* statfs */
+};
+
+static struct file_operations shm_root_operations = {
+	NULL,                   /* llseek */
+	NULL,                   /* read */
+	NULL,                   /* write */
+	shm_readdir,		/* readdir */
+};
+
+static struct inode_operations shm_root_inode_operations = {
+	&shm_root_operations,	/* file operations */
+	shm_create,		/* create */
+	shm_lookup,		/* lookup */
+	NULL,			/* link */
+	shm_unlink,		/* unlink */
+};
+
+static struct file_operations shm_file_operations = {
+	NULL,			/* llseek */
+	NULL,			/* read */
+	NULL,			/* write */
+	NULL,			/* readdir */
+	NULL,			/* poll */
+	NULL,			/* ioctl */
+	shm_mmap,		/* mmap */
+};
+
+static struct inode_operations shm_inode_operations = {
+	&shm_file_operations,	/* file operations */
+};
+
+static struct vm_operations_struct shm_vm_ops = {
+	shm_open,		/* open - callback for a new vm-area open */
+	shm_close,		/* close - callback for when the vm-area is released */
+	NULL,			/* no need to sync pages at unmap */
+	NULL,			/* protect */
+	NULL,			/* sync */
+	NULL,			/* advise */
+	shm_nopage,		/* nopage */
+	NULL,			/* wppage */
+	shm_swapout		/* swapout */
+};
+
 size_t shm_ctlmax = SHMMAX;
 int shm_ctlall = SHMALL;
 int shm_ctlmni = SHMMNI;
@@ -75,7 +164,7 @@
 	pagecache_lock
 	shm_lock()/shm_lockall()
 	kernel lock
-	shp->sem
+	inode->i_sem
 	sem_ids.sem
 	mmap_sem
 
@@ -94,12 +183,231 @@
 void __init shm_init (void)
 {
 	ipc_init_ids(&shm_ids, shm_ctlmni);
+
+	register_filesystem (&shm_fs_type);
 #ifdef CONFIG_PROC_FS
 	create_proc_read_entry("sysvipc/shm", 0, 0, sysvipc_shm_read_proc, NULL);
 #endif
 	return;
 }
 
+static struct super_block *shm_read_super(struct super_block *s,void *data, 
+					  int silent)
+{
+	struct inode * root_inode;
+
+	if (shm_sb) {
+		printk ("shm fs already mounted\n");
+		return NULL;
+	}
+
+	lock_super(s);
+	s->s_blocksize = PAGE_SIZE;
+	s->s_blocksize_bits = PAGE_SHIFT;
+	s->s_magic = 0;
+	s->s_op = &shm_sops;
+	root_inode = iget (s, SEQ_MULTIPLIER);
+	if (!root_inode)
+		goto out_no_root;
+	root_inode->i_op = &shm_root_inode_operations;
+	root_inode->i_sb = s;
+	root_inode->i_nlink = 2;
+	root_inode->i_mode = S_IFDIR | S_IRWXUGO | S_ISVTX;
+	s->s_root = d_alloc_root(root_inode);
+	if (!s->s_root)
+		goto out_no_root;
+	s->u.generic_sbp = (void*) shm_sb;
+	shm_sb = s;
+	unlock_super(s);
+	return s;
+
+out_no_root:
+	printk("proc_read_super: get root inode failed\n");
+	iput(root_inode);
+	s->s_dev = 0;
+	unlock_super(s);
+	return NULL;
+}
+
+static void shm_put_super(struct super_block *sb)
+{
+	struct super_block **p = &shm_sb;
+	while (*p != sb) {
+		if (!*p)	/* should never happen */
+			return;
+		p = (struct super_block **)&(*p)->u.generic_sbp;
+	}
+	*p = (struct super_block *)(*p)->u.generic_sbp;
+	down(&shm_ids.sem);
+	kfree (ipc_path);
+	ipc_path = NULL;
+	up(&shm_ids.sem);
+}
+
+static int shm_statfs(struct super_block *sb, struct statfs *buf, int bufsiz)
+{
+	struct statfs tmp;
+
+	tmp.f_type = 0;
+	tmp.f_bsize = PAGE_SIZE;
+	tmp.f_blocks = shm_ctlall;
+	tmp.f_bavail = tmp.f_bfree = shm_ctlall - shm_tot;
+	tmp.f_files = shm_ctlmni;
+	tmp.f_ffree = shm_ctlmni - used_segs;
+	tmp.f_namelen = SHM_NAME_LEN;
+	return copy_to_user(buf, &tmp, bufsiz) ? -EFAULT : 0;
+}
+
+static void shm_write_inode(struct inode * inode)
+{
+}
+
+static void shm_read_inode(struct inode * inode)
+{
+	int id;
+	struct shmid_kernel *shp;
+
+	id = inode->i_ino;
+	inode->i_op = NULL;
+	inode->i_mode = 0;
+
+	if (!(shp = shm_lock (id)))
+		return;
+	inode->i_mode = shp->u.shm_perm.mode | S_IFREG;
+	inode->i_uid  = shp->u.shm_perm.uid;
+	inode->i_gid  = shp->u.shm_perm.gid;
+	inode->i_size = shp->u.shm_segsz;
+	shm_unlock (id);
+	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+	inode->i_op  = &shm_inode_operations;
+}
+
+static int shm_create (struct inode *dir, struct dentry *dent, int mode)
+{
+	int id, err;
+	struct inode * inode;
+
+	down(&shm_ids.sem);
+	err = id = newseg (IPC_PRIVATE, dent->d_name.name, dent->d_name.len, mode, 0);
+	if (err < 0)
+		goto out;
+
+	err = -ENOMEM;
+	inode = iget (shm_sb, id % SEQ_MULTIPLIER);
+	if (!inode)
+		goto out;
+
+	err = 0;
+	down (&inode->i_sem);
+	inode->i_mode = mode | S_IFREG;
+	inode->i_op   = &shm_inode_operations;
+	d_instantiate(dent, inode);
+	up (&inode->i_sem);
+
+out:
+	up(&shm_ids.sem);
+	return err;
+}
+
+static int shm_readdir (struct file *filp, void *dirent, filldir_t filldir)
+{
+	struct inode * inode = filp->f_dentry->d_inode;
+	struct shmid_kernel *shp;
+	off_t nr;
+
+	nr = filp->f_pos;
+
+	switch(nr)
+	{
+	case 0:
+		if (filldir(dirent, ".", 1, nr, inode->i_ino) < 0)
+			return 0;
+		filp->f_pos = ++nr;
+		/* fall through */
+	case 1:
+		if (filldir(dirent, "..", 2, nr, inode->i_ino) < 0)
+			return 0;
+		filp->f_pos = ++nr;
+		/* fall through */
+	default:
+		down(&shm_ids.sem);
+		for (; nr-2 <= shm_ids.max_id; nr++ ) {
+			if (!(shp = shm_get (nr-2))) 
+				continue;
+			if (shp->u.shm_perm.mode & SHM_DEST)
+				continue;
+			if (filldir(dirent, shp->name, shp->namelen, nr, nr) < 0 )
+				break;;
+		}
+		filp->f_pos = nr;
+		up(&shm_ids.sem);
+		break;
+	}
+
+	UPDATE_ATIME(inode);
+	return 0;
+}
+
+static struct dentry *shm_lookup (struct inode *dir, struct dentry *dent)
+{
+	int i, err = 0;
+	struct shmid_kernel* shp;
+	struct inode *inode = NULL;
+
+	if (dent->d_name.len > SHM_NAME_LEN)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	down(&shm_ids.sem);
+	for(i = 0; i <= shm_ids.max_id; i++) {
+		if (!(shp = shm_lock(i)))
+		    continue;
+		if (!(shp->u.shm_perm.mode & SHM_DEST) &&
+		    dent->d_name.len == shp->namelen &&
+		    strncmp(dent->d_name.name, shp->name, shp->namelen) == 0)
+			goto found;
+		shm_unlock(i);
+	}
+
+	/*
+	 * prevent the reserved names as negative dentries. 
+	 * This also prevents object creation through the filesystem
+	 */
+	if (dent->d_name.len == SHM_FMT_LEN &&
+	    memcmp (SHM_FMT, dent->d_name.name, SHM_FMT_LEN - 8) == 0)
+		err = -EACCES;	
+
+	goto out;
+
+found:
+	shm_unlock(i);
+	inode = iget(dir->i_sb, i);
+
+	if (!inode)
+		err = -EACCES;
+out:
+	if (err == 0)
+		d_add (dent, inode);
+	up (&shm_ids.sem);
+	return ERR_PTR(err);
+}
+
+static int shm_unlink (struct inode *dir, struct dentry *dent)
+{
+	struct inode * inode = dent->d_inode;
+	struct shmid_kernel *shp;
+
+	down (&shm_ids.sem);
+	if (!(shp = shm_lock (inode->i_ino)))
+		BUG();
+	shp->u.shm_perm.mode |= SHM_DEST;
+	shp->u.shm_perm.key = IPC_PRIVATE; /* Do not find it any more */
+	shm_unlock (inode->i_ino);
+	up (&shm_ids.sem);
+	inode->i_nlink -= 1;
+	d_delete (dent);
+	return 0;
+}
+
 #define SHM_ENTRY(shp, index) (shp)->shm_dir[(index)/PTRS_PER_PTE][(index)%PTRS_PER_PTE]
 
 static pte_t **shm_alloc(unsigned long pages)
@@ -108,9 +416,12 @@
 	unsigned short last = pages % PTRS_PER_PTE;
 	pte_t **ret, **ptr;
 
+	if (pages == 0)
+		return NULL;
+
 	ret = kmalloc ((dir+1) * sizeof(pte_t *), GFP_KERNEL);
 	if (!ret)
-		goto out;
+		goto nomem;
 
 	for (ptr = ret; ptr < ret+dir ; ptr++)
 	{
@@ -127,7 +438,6 @@
 			goto free;
 		memset (*ptr, 0, last*sizeof(pte_t));
 	}
-out:	
 	return ret;
 
 free:
@@ -136,66 +446,111 @@
 		free_page ((unsigned long)*ptr);
 
 	kfree (ret);
-	return NULL;
+nomem:
+	return ERR_PTR(-ENOMEM);
 }
 
-
 static void shm_free(pte_t** dir, unsigned long pages)
 {
 	pte_t **ptr = dir+pages/PTRS_PER_PTE;
 
+	if (!dir)
+		return;
+
 	/* first the last page */
 	if (pages%PTRS_PER_PTE)
 		kfree (*ptr);
 	/* now the whole pages */
 	while (--ptr >= dir)
-		free_page ((unsigned long)*ptr);
+		if (*ptr)
+			free_page ((unsigned long)*ptr);
 
 	/* Now the indirect block */
 	kfree (dir);
 }
 
-static int shm_revalidate(struct shmid_kernel* shp, int shmid, int pagecount, int flg)
+static 	int shm_notify (struct dentry *dentry, struct iattr *attr)
 {
-	struct shmid_kernel* new;
-	new = shm_lock(shmid);
-	if(new==NULL) {
-		return -EIDRM;
-	}
-	if(new!=shp || shm_checkid(shp, shmid) || shp->shm_npages != pagecount) {
-		shm_unlock(shmid);
-		return -EIDRM;
-	}
-	if (ipcperms(&shp->u.shm_perm, flg)) {
-		shm_unlock(shmid);
-		return -EACCES;
+	int error;
+	struct inode *inode = dentry->d_inode;
+	struct shmid_kernel *shp;
+	unsigned long new_pages, old_pages;
+	pte_t **new_dir, **old_dir;
+
+	if ((error = inode_change_ok(inode, attr)))
+		return error;
+	if (!(attr->ia_valid & ATTR_SIZE))
+		goto set_attr;
+	if (attr->ia_size > shm_ctlmax)
+		return -EFBIG;
+
+	/* We set old_pages and old_dir for easier cleanup */
+	old_pages = new_pages = (attr->ia_size  + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	if (shm_tot + new_pages >= shm_ctlall)
+		return -ENOSPC;
+	if (IS_ERR(old_dir = new_dir = shm_alloc(new_pages)))
+		return PTR_ERR(new_dir);
+
+	if (!(shp = shm_lock(inode->i_ino)))
+		BUG();
+	if (shp->u.shm_segsz == attr->ia_size)
+		goto out;
+	old_dir = shp->shm_dir;
+	old_pages = shp->shm_npages;
+	if (old_dir){
+		pte_t *swap;
+		int i,j;
+		i = old_pages < new_pages ? old_pages : new_pages;
+		j = i % PTRS_PER_PTE;
+		i /= PTRS_PER_PTE;
+		if (j)
+			memcpy (new_dir[i], old_dir[i], j * sizeof (pte_t));
+		while (i--) {
+			swap = new_dir[i];
+			new_dir[i] = old_dir[i];
+			old_dir[i] = swap;
+		}
 	}
+	shp->shm_dir = new_dir;
+	shp->shm_npages = new_pages;
+	shp->u.shm_segsz = attr->ia_size;
+out:
+	shm_unlock(inode->i_ino);
+	shm_lockall();
+	shm_tot += new_pages - old_pages;
+	shm_unlockall();
+	shm_free (old_dir, old_pages);
+set_attr:
+	inode_setattr(inode, attr);
 	return 0;
 }
 
-static int newseg (key_t key, int shmflg, size_t size)
+static int newseg (key_t key, const char *name, int namelen,
+		   int shmflg, size_t size)
 {
 	struct shmid_kernel *shp;
 	int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
 	int id;
 
-	if (size < SHMMIN)
-		return -EINVAL;
+	if (namelen > SHM_NAME_LEN)
+		return -ENAMETOOLONG;
 
 	if (size > shm_ctlmax)
 		return -EINVAL;
 	if (shm_tot + numpages >= shm_ctlall)
 		return -ENOSPC;
 
-	shp = (struct shmid_kernel *) kmalloc (sizeof (*shp), GFP_KERNEL);
+	shp = (struct shmid_kernel *) 
+		kmalloc (sizeof (*shp) + (namelen ? namelen : SHM_FMT_LEN + 1), GFP_KERNEL);
 	if (!shp)
 		return -ENOMEM;
 
-	shp->shm_dir = shm_alloc (numpages);
-	if (!shp->shm_dir) {
+	if (IS_ERR(shp->shm_dir = shm_alloc (numpages))){
+		int error = PTR_ERR(shp->shm_dir);
 		kfree(shp);
-		return -ENOMEM;
+		return error;
 	}
+
 	id = ipc_addid(&shm_ids, &shp->u.shm_perm, shm_ctlmni);
 	if(id == -1) {
 		shm_free(shp->shm_dir,numpages);
@@ -206,18 +561,25 @@
 	shp->u.shm_perm.mode = (shmflg & S_IRWXUGO);
 	shp->u.shm_segsz = size;
 	shp->u.shm_cpid = current->pid;
-	shp->attaches = NULL;
-	shp->u.shm_lpid = shp->u.shm_nattch = 0;
+	shp->u.shm_lpid = 0;
 	shp->u.shm_atime = shp->u.shm_dtime = 0;
 	shp->u.shm_ctime = CURRENT_TIME;
+	shp->u.shm_nattch = 0;
 	shp->shm_npages = numpages;
-	shp->id = shm_buildid(id,shp->u.shm_perm.seq);
-	init_MUTEX(&shp->sem);
+	id = shm_buildid(id,shp->u.shm_perm.seq);
+	if (namelen != 0) {
+		shp->namelen = namelen;
+		memcpy (shp->name, name, namelen);		  
+	} else {
+		shp->namelen = sprintf (shp->name, SHM_FMT, id);
+	}
 
 	shm_tot += numpages;
+	used_segs++;
+	shm_sb->s_root->d_inode->i_size++;
 	shm_unlock(id);
-
-	return shm_buildid(id,shp->u.shm_perm.seq);
+	
+	return id;
 }
 
 asmlinkage long sys_shmget (key_t key, size_t size, int shmflg)
@@ -225,14 +587,22 @@
 	struct shmid_kernel *shp;
 	int err, id = 0;
 
+	if (!shm_sb) {
+		printk ("shmget: shm filesystem not mounted\n");
+		return -EINVAL;
+	}
+
+	if (size < SHMMIN)
+		return -EINVAL;
+
 	down(&shm_ids.sem);
 	if (key == IPC_PRIVATE) {
-		err = newseg(key, shmflg, size);
+		err = newseg(key, NULL, 0, shmflg, size);
 	} else if ((id = ipc_findkey(&shm_ids,key)) == -1) {
 		if (!(shmflg & IPC_CREAT))
 			err = -ENOENT;
 		else
-			err = newseg(key, shmflg, size);
+			err = newseg(key, NULL, 0, shmflg, size);
 	} else if ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) {
 		err = -EEXIST;
 	} else {
@@ -249,12 +619,9 @@
 	return err;
 }
 
-/*
- * Only called after testing nattch and SHM_DEST.
- * Here pages, pgtable and shmid_kernel are freed.
- */
-static void killseg (int shmid)
+static void shm_delete (struct inode *ino)
 {
+	int shmid = ino->i_ino;
 	struct shmid_kernel *shp;
 	int i, numpages;
 	int rss, swp;
@@ -262,20 +629,9 @@
 	down(&shm_ids.sem);
 	shp = shm_lock(shmid);
 	if(shp==NULL) {
-out_up:
-		up(&shm_ids.sem);
-		return;
-	}
-	if(shm_checkid(shp,shmid) || shp->u.shm_nattch > 0 ||
-	    !(shp->u.shm_perm.mode & SHM_DEST)) {
-		shm_unlock(shmid);
-		goto out_up;
+		BUG();
 	}
 	shp = shm_rmid(shmid);
-	if(shp==NULL)
-		BUG();
-	if (!shp->shm_dir)
-		BUG();
 	shm_unlock(shmid);
 	up(&shm_ids.sem);
 
@@ -299,16 +655,49 @@
 	shm_rss -= rss;
 	shm_swp -= swp;
 	shm_tot -= numpages;
+	shm_sb->s_root->d_inode->i_size--;
+	used_segs--;
 	shm_unlockall();
 	return;
 }
 
+char * shm_getname(int id)
+{
+	char *result;
+
+	result = __getname ();
+	if (IS_ERR(result))
+		return result;
+
+	down(&shm_ids.sem);
+	if (!ipc_path) {
+		char *tmp = d_path (shm_sb->s_root, result, PAGE_SIZE);
+		ipc_path = kmalloc (strlen(tmp) + sizeof (SHM_FMT) + 1,
+				     GFP_KERNEL);
+		if (!ipc_path) {
+			putname (result);
+			up (&shm_ids.sem);
+			return ERR_PTR(-ENOMEM);
+		}
+
+		sprintf (ipc_path, "%s/%s", tmp, SHM_FMT);
+	}
+	sprintf (result, ipc_path, id); 
+	up(&shm_ids.sem);
+	return result;
+}
+
 asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds *buf)
 {
 	struct shmid_ds tbuf;
 	struct shmid_kernel *shp;
 	int err;
 
+	if (!shm_sb) {
+		printk ("shmctl: shm filesystem not mounted\n");
+		return -EINVAL;
+	}
+
 	if (cmd < 0 || shmid < 0)
 		return -EINVAL;
 
@@ -410,48 +799,48 @@
 		return err;
 	}
 	case IPC_RMID:
-	case IPC_SET:
-		break;
-	default:
-		return -EINVAL;
+	{
+		char *name = shm_getname(shmid);
+		if (IS_ERR(name))
+			return PTR_ERR(name);
+		lock_kernel();
+		err = do_unlink (name);
+		unlock_kernel();
+		putname (name);
+		if (err == -ENOENT)
+			err = -EINVAL;
+		return err;
 	}
-
-	if (cmd == IPC_SET) {
+	case IPC_SET:
+	{
 		if(copy_from_user (&tbuf, buf, sizeof (*buf)))
 			return -EFAULT;
-	}
-	down(&shm_ids.sem);
-	shp = shm_lock(shmid);
-	err=-EINVAL;
-	if(shp==NULL)
-		goto out_up;
-	err=-EIDRM;
-	if(shm_checkid(shp,shmid))
-		goto out_unlock_up;
-	err=-EPERM;
-	if (current->euid != shp->u.shm_perm.uid &&
-	    current->euid != shp->u.shm_perm.cuid && 
-	    !capable(CAP_SYS_ADMIN)) {
-		goto out_unlock_up;
-	}
+		down(&shm_ids.sem);
+		shp = shm_lock(shmid);
+		err=-EINVAL;
+		if(shp==NULL)
+			goto out_up;
+		err=-EIDRM;
+		if(shm_checkid(shp,shmid))
+			goto out_unlock_up;
+		err=-EPERM;
+		if (current->euid != shp->u.shm_perm.uid &&
+		    current->euid != shp->u.shm_perm.cuid && 
+		    !capable(CAP_SYS_ADMIN))
+			goto out_unlock_up;
 
-	switch (cmd) {
-	case IPC_SET:
 		shp->u.shm_perm.uid = tbuf.shm_perm.uid;
 		shp->u.shm_perm.gid = tbuf.shm_perm.gid;
 		shp->u.shm_perm.mode = (shp->u.shm_perm.mode & ~S_IRWXUGO)
 			| (tbuf.shm_perm.mode & S_IRWXUGO);
 		shp->u.shm_ctime = CURRENT_TIME;
 		break;
-	case IPC_RMID:
-		shp->u.shm_perm.mode |= SHM_DEST;
-		if (shp->u.shm_nattch <= 0) {
-			shm_unlock(shmid);
-			up(&shm_ids.sem);
-			killseg (shmid);
-			return 0;
-		}
 	}
+
+	default:
+		return -EINVAL;
+	}
+
 	err = 0;
 out_unlock_up:
 	shm_unlock(shmid);
@@ -463,70 +852,24 @@
 	return err;
 }
 
-/*
- * The per process internal structure for managing segments is
- * `struct vm_area_struct'.
- * A shmat will add to and shmdt will remove from the list.
- * shmd->vm_mm		the attacher
- * shmd->vm_start	virt addr of attach, multiple of SHMLBA
- * shmd->vm_end		multiple of SHMLBA
- * shmd->vm_next	next attach for task
- * shmd->vm_next_share	next attach for segment
- * shmd->vm_pgoff	offset into segment (in pages)
- * shmd->vm_private_data		signature for this attach
- */
-
-static struct vm_operations_struct shm_vm_ops = {
-	shm_open,		/* open - callback for a new vm-area open */
-	shm_close,		/* close - callback for when the vm-area is released */
-	NULL,			/* no need to sync pages at unmap */
-	NULL,			/* protect */
-	NULL,			/* sync */
-	NULL,			/* advise */
-	shm_nopage,		/* nopage */
-	NULL,			/* wppage */
-	shm_swapout		/* swapout */
-};
-
-/* Insert shmd into the list shp->attaches */
-static inline void insert_attach (struct shmid_kernel * shp, struct vm_area_struct * shmd)
-{
-	if((shmd->vm_next_share = shp->attaches) != NULL)
-		shp->attaches->vm_pprev_share = &shmd->vm_next_share;
-	shp->attaches = shmd;
-	shmd->vm_pprev_share = &shp->attaches;
-}
+static inline void shm_inc (int id) {
+	struct shmid_kernel *shp;
 
-/* Remove shmd from list shp->attaches */
-static inline void remove_attach (struct shmid_kernel * shp, struct vm_area_struct * shmd)
-{
-	if(shmd->vm_next_share)
-		shmd->vm_next_share->vm_pprev_share = shmd->vm_pprev_share;
-	*shmd->vm_pprev_share = shmd->vm_next_share;
+	if(!(shp = shm_lock(id)))
+		BUG();
+	shp->u.shm_atime = CURRENT_TIME;
+	shp->u.shm_lpid = current->pid;
+	shp->u.shm_nattch++;
+	shm_unlock(id);
 }
 
-/*
- * ensure page tables exist
- * mark page table entries with shm_sgn.
- */
-static int shm_map (struct vm_area_struct *shmd)
+static int shm_mmap(struct file * file, struct vm_area_struct * vma)
 {
-	unsigned long tmp;
-
-	/* clear old mappings */
-	do_munmap(shmd->vm_start, shmd->vm_end - shmd->vm_start);
-
-	/* add new mapping */
-	tmp = shmd->vm_end - shmd->vm_start;
-	if((current->mm->total_vm << PAGE_SHIFT) + tmp
-	   > (unsigned long) current->rlim[RLIMIT_AS].rlim_cur)
-		return -ENOMEM;
-	current->mm->total_vm += tmp >> PAGE_SHIFT;
-	vmlist_modify_lock(current->mm);
-	insert_vm_struct(current->mm, shmd);
-	merge_segments(current->mm, shmd->vm_start, shmd->vm_end);
-	vmlist_modify_unlock(current->mm);
-
+	if (!(vma->vm_flags & VM_SHARED))
+		return -EINVAL; /* we cannot do private mappings */
+	UPDATE_ATIME(file->f_dentry->d_inode);
+	vma->vm_ops = &shm_vm_ops;
+	shm_inc(file->f_dentry->d_inode->i_ino);
 	return 0;
 }
 
@@ -535,135 +878,57 @@
  */
 asmlinkage long sys_shmat (int shmid, char *shmaddr, int shmflg, ulong *raddr)
 {
-	struct shmid_kernel *shp;
-	struct vm_area_struct *shmd;
-	int err;
 	unsigned long addr;
-	unsigned long len;
-	short flg = shmflg & SHM_RDONLY ? S_IRUGO : S_IRUGO|S_IWUGO;
-
+	struct file * file;
+	int    err;
+	int    flags;
+	char   *name;
 
-	if (shmid < 0)
+	if (!shm_sb)
 		return -EINVAL;
 
-	down(&current->mm->mmap_sem);
-	err = -EINVAL;
-	shp = shm_lock(shmid);
-	if (!shp)
-		goto out_up;
-
-	err = -EACCES;
-	if (ipcperms(&shp->u.shm_perm, flg))
-		goto out_unlock_up;
-
-	err = -EIDRM;
-	if (shm_checkid(shp,shmid))
-		goto out_unlock_up;
-
-	if (!(addr = (ulong) shmaddr)) {
-		if (shmflg & SHM_REMAP)
-			goto out_unlock_up;
-		err = -ENOMEM;
-		addr = 0;
-	again:
-		if (!(addr = get_unmapped_area(addr, (unsigned long)shp->u.shm_segsz)))
-			goto out_unlock_up;
-		if(addr & (SHMLBA - 1)) {
-			addr = (addr + (SHMLBA - 1)) & ~(SHMLBA - 1);
-			goto again;
+	if ((addr = (ulong)shmaddr))
+	{
+		if(addr & (SHMLBA-1)) {
+			if (shmflg & SHM_RND)
+				addr &= ~(SHMLBA-1);	   /* round down */
+			else
+				return -EINVAL;
 		}
-	} else if (addr & (SHMLBA-1)) {
-		err=-EINVAL;
-		if (shmflg & SHM_RND)
-			addr &= ~(SHMLBA-1);       /* round down */
-		else
-			goto out_unlock_up;
-	}
-	/*
-	 * Check if addr exceeds TASK_SIZE (from do_mmap)
-	 */
-	len = PAGE_SIZE*shp->shm_npages;
-	err = -EINVAL;
-	if (addr >= TASK_SIZE || len > TASK_SIZE  || addr > TASK_SIZE - len)
-		goto out_unlock_up;
-	/*
-	 * If shm segment goes below stack, make sure there is some
-	 * space left for the stack to grow (presently 4 pages).
-	 */
-	if (addr < current->mm->start_stack &&
-	    addr > current->mm->start_stack - PAGE_SIZE*(shp->shm_npages + 4))
-		goto out_unlock_up;
-	if (!(shmflg & SHM_REMAP) && find_vma_intersection(current->mm, addr, addr + (unsigned long)shp->u.shm_segsz))
-		goto out_unlock_up;
-
-	shm_unlock(shmid);
-	err = -ENOMEM;
-	shmd = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
-	err = shm_revalidate(shp, shmid, len/PAGE_SIZE,flg);
-	if(err)	{
-		kmem_cache_free(vm_area_cachep, shmd);
-		goto out_up;
-	}
-
-	shmd->vm_private_data = shp;
-	shmd->vm_start = addr;
-	shmd->vm_end = addr + shp->shm_npages * PAGE_SIZE;
-	shmd->vm_mm = current->mm;
-	shmd->vm_page_prot = (shmflg & SHM_RDONLY) ? PAGE_READONLY : PAGE_SHARED;
-	shmd->vm_flags = VM_SHM | VM_MAYSHARE | VM_SHARED
-			 | VM_MAYREAD | VM_MAYEXEC | VM_READ | VM_EXEC
-			 | ((shmflg & SHM_RDONLY) ? 0 : VM_MAYWRITE | VM_WRITE);
-	shmd->vm_file = NULL;
-	shmd->vm_pgoff = 0;
-	shmd->vm_ops = &shm_vm_ops;
-
-	shp->u.shm_nattch++;	    /* prevent destruction */
-	shm_unlock(shp->id);
-	err = shm_map (shmd);
-	shm_lock(shmid); /* cannot fail */
-	if (err)
-		goto failed_shm_map;
-
-	insert_attach(shp,shmd);  /* insert shmd into shp->attaches */
-
-	shp->u.shm_lpid = current->pid;
-	shp->u.shm_atime = CURRENT_TIME;
+		flags = MAP_SHARED | MAP_FIXED;
+	} else
+		flags = MAP_SHARED;
 
-	*raddr = addr;
-	err = 0;
-out_unlock_up:
-	shm_unlock(shmid);
-out_up:
-	up(&current->mm->mmap_sem);
+	name = shm_getname(shmid);
+	if (IS_ERR (name))
+		return PTR_ERR (name);
+
+	file = filp_open (name, O_RDWR, 0);
+	putname (name);
+	if (IS_ERR (file))
+		goto bad_file;
+	lock_kernel();
+	*raddr = do_mmap (file, addr, file->f_dentry->d_inode->i_size,
+			  (shmflg & SHM_RDONLY ? PROT_READ :
+			   PROT_READ | PROT_WRITE), flags, 0);
+	unlock_kernel();
+	if (IS_ERR(*raddr))
+		err = PTR_ERR(*raddr);
+	else
+		err = 0;
+        fput (file);
 	return err;
 
-failed_shm_map:
-	{
-		int delete = 0;
-		if (--shp->u.shm_nattch <= 0 && shp->u.shm_perm.mode & SHM_DEST)
-			delete = 1;
-		shm_unlock(shmid);
-		up(&current->mm->mmap_sem);
-		kmem_cache_free(vm_area_cachep, shmd);
-		if(delete)
-			killseg(shmid);
-		return err;
-	}
+bad_file:
+	if ((err = PTR_ERR(file)) == -ENOENT)
+		return -EINVAL;
+	return err;
 }
 
 /* This is called by fork, once for every shm attach. */
 static void shm_open (struct vm_area_struct *shmd)
 {
-	struct shmid_kernel *shp;
-
-	shp = (struct shmid_kernel *) shmd->vm_private_data;
-	if(shp != shm_lock(shp->id))
-		BUG();
-	insert_attach(shp,shmd);  /* insert shmd into shp->attaches */
-	shp->u.shm_nattch++;
-	shp->u.shm_atime = CURRENT_TIME;
-	shp->u.shm_lpid = current->pid;
-	shm_unlock(shp->id);
+	shm_inc (shmd->vm_file->f_dentry->d_inode->i_ino);
 }
 
 /*
@@ -674,22 +939,16 @@
  */
 static void shm_close (struct vm_area_struct *shmd)
 {
+	int id = shmd->vm_file->f_dentry->d_inode->i_ino;
 	struct shmid_kernel *shp;
-	int id;
 
 	/* remove from the list of attaches of the shm segment */
-	shp = (struct shmid_kernel *) shmd->vm_private_data;
-	if(shp != shm_lock(shp->id))
+	if(!(shp = shm_lock(id)))
 		BUG();
-	remove_attach(shp,shmd);  /* remove from shp->attaches */
-  	shp->u.shm_lpid = current->pid;
+	shp->u.shm_lpid = current->pid;
 	shp->u.shm_dtime = CURRENT_TIME;
-	id=-1;
-	if (--shp->u.shm_nattch <= 0 && shp->u.shm_perm.mode & SHM_DEST)
-		id=shp->id;
-	shm_unlock(shp->id);
-	if(id!=-1)
-		killseg(id);
+	shp->u.shm_nattch--;
+	shm_unlock(id);
 }
 
 /*
@@ -733,32 +992,35 @@
 	struct shmid_kernel *shp;
 	unsigned int idx;
 	struct page * page;
+	struct inode * inode = shmd->vm_file->f_dentry->d_inode;
 
-	shp = (struct shmid_kernel *) shmd->vm_private_data;
 	idx = (address - shmd->vm_start) >> PAGE_SHIFT;
 	idx += shmd->vm_pgoff;
 
-	down(&shp->sem);
-	if(shp != shm_lock(shp->id))
+	down(&inode->i_sem);
+	if(!(shp = shm_lock(inode->i_ino)))
 		BUG();
 
+	if (idx >= shp->shm_npages)
+		goto sigbus;
+
 	pte = SHM_ENTRY(shp,idx);
 	if (!pte_present(pte)) {
 		/* page not present so shm_swap can't race with us
 		   and the semaphore protects us by other tasks that
 		   could potentially fault on our pte under us */
 		if (pte_none(pte)) {
-			shm_unlock(shp->id);
+			shm_unlock(inode->i_ino);
 			page = alloc_page(GFP_HIGHUSER);
 			if (!page)
 				goto oom;
 			clear_highpage(page);
-			if(shp != shm_lock(shp->id))
+			if(shp != shm_lock(inode->i_ino))
 				BUG();
 		} else {
 			swp_entry_t entry = pte_to_swp_entry(pte);
 
-			shm_unlock(shp->id);
+			shm_unlock(inode->i_ino);
 			page = lookup_swap_cache(entry);
 			if (!page) {
 				lock_kernel();
@@ -771,7 +1033,7 @@
 			delete_from_swap_cache(page);
 			page = replace_with_highmem(page);
 			swap_free(entry);
-			if(shp != shm_lock(shp->id))
+			if(shp != shm_lock(inode->i_ino))
 				BUG();
 			shm_swp--;
 		}
@@ -783,14 +1045,18 @@
 
 	/* pte_val(pte) == SHM_ENTRY (shp, idx) */
 	get_page(pte_page(pte));
-	shm_unlock(shp->id);
-	up(&shp->sem);
+	shm_unlock(inode->i_ino);
+	up(&inode->i_sem);
 	current->min_flt++;
 	return pte_page(pte);
 
 oom:
-	up(&shp->sem);
+	up(&inode->i_sem);
 	return NOPAGE_OOM;
+sigbus:
+	shm_unlock(inode->i_ino);
+	up(&inode->i_sem);
+	return NOPAGE_SIGBUS;
 }
 
 /*
@@ -938,20 +1204,20 @@
 	int i, len = 0;
 
 	down(&shm_ids.sem);
-	len += sprintf(buffer, "       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime\n");
+	len += sprintf(buffer, "       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime name\n");
 
-    	for(i = 0; i <= shm_ids.max_id; i++) {
+	for(i = 0; i <= shm_ids.max_id; i++) {
 		struct shmid_kernel* shp = shm_lock(i);
 		if(shp!=NULL) {
-#define SMALL_STRING "%10d %10d  %4o %10u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
-#define BIG_STRING   "%10d %10d  %4o %21u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
+#define SMALL_STRING "%10d %10d  %4o %10u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu %.*s\n"
+#define BIG_STRING   "%10d %10d  %4o %21u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu %.*s\n"
 			char *format;
 
 			if (sizeof(size_t) <= sizeof(int))
 				format = SMALL_STRING;
 			else
 				format = BIG_STRING;
-	    		len += sprintf(buffer + len, format,
+			len += sprintf(buffer + len, format,
 				shp->u.shm_perm.key,
 				shm_buildid(i, shp->u.shm_perm.seq),
 				shp->u.shm_perm.mode,
@@ -965,7 +1231,9 @@
 				shp->u.shm_perm.cgid,
 				shp->u.shm_atime,
 				shp->u.shm_dtime,
-				shp->u.shm_ctime);
+				shp->u.shm_ctime,
+				shp->namelen,
+				shp->name);
 			shm_unlock(i);
 
 			pos += len;
diff -uNr 2.3.38/mm/mmap.c c38/mm/mmap.c
--- 2.3.38/mm/mmap.c	Thu Dec 23 20:41:46 1999
+++ c38/mm/mmap.c	Sun Jan  9 11:47:23 2000
@@ -271,7 +271,6 @@
 	vma->vm_ops = NULL;
 	vma->vm_pgoff = pgoff;
 	vma->vm_file = NULL;
-	vma->vm_private_data = NULL;
 
 	/* Clear old maps */
 	error = -ENOMEM;
@@ -547,7 +546,6 @@
 		mpnt->vm_ops = area->vm_ops;
 		mpnt->vm_pgoff = area->vm_pgoff + ((end - area->vm_start) >> PAGE_SHIFT);
 		mpnt->vm_file = area->vm_file;
-		mpnt->vm_private_data = area->vm_private_data;
 		if (mpnt->vm_file)
 			get_file(mpnt->vm_file);
 		if (mpnt->vm_ops && mpnt->vm_ops->open)
@@ -780,7 +778,6 @@
 	vma->vm_ops = NULL;
 	vma->vm_pgoff = 0;
 	vma->vm_file = NULL;
-	vma->vm_private_data = NULL;
 
 	/*
 	 * merge_segments may merge our vma, so we can't refer to it
@@ -927,7 +924,6 @@
 
 		/* To share, we must have the same file, operations.. */
 		if ((mpnt->vm_file != prev->vm_file)||
-		    (mpnt->vm_private_data != prev->vm_private_data)	||
 		    (mpnt->vm_ops != prev->vm_ops)	||
 		    (mpnt->vm_flags != prev->vm_flags)	||
 		    (prev->vm_end != mpnt->vm_start))

Re: [PATCH] replace SYSV shared memory with shm filesystem

[Alan Cox]

> replaces/reuses the existing SYSV shm code so you now have to mount
> the fs to be able to use SYSV SHM. But in turn we now have everything
> in place to implement posix shm. This also obsoletes vm_private_data
> in vm_area_struct.

Umm no. It obsoletes vm_private_data for existing merged file systems. The stackable
file systems still need this field (cryptfs, lofs etc)

> Also it is now possible to do e.g. 'rm /dev/shm/*' instead of this
> terrible 'ipcrm shm xx' :-)

Nice

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Re: [PATCH] replace SYSV shared memory with shm filesystem

[Christoph Rohland]

Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

> > replaces/reuses the existing SYSV shm code so you now have to
> > mount the fs to be able to use SYSV SHM. But in turn we now have
> > everything in place to implement posix shm. This also obsoletes
> > vm_private_data in vm_area_struct.
> 
> Umm no. It obsoletes vm_private_data for existing merged file
> systems. The stackable file systems still need this field (cryptfs,
> lofs etc)

Hey, that's a pity :-( I liked this cleanup. Do they really need it?

> > Also it is now possible to do e.g. 'rm /dev/shm/*' instead of this
> >terrible 'ipcrm shm xx' :-)
> 
> Nice

Yup :-)

Greetings
		Christoph
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Re: [PATCH] replace SYSV shared memory with shm filesystem

[Rik van Riel]

On 10 Jan 2000, Christoph Rohland wrote:

> You can mount the fs only once. This will probably break shm in
> chrooted environments.

I think it would be best to code it in such a way that you
can mount multiple instances of shmfs, in such a way that
the differently chrooted programs cannot see each other's
shared memory. That should make it a bit more difficult to
get out of a chroot() jail...

(security buffs, please tell me if I'm full of it)

cheers,

Rik
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Re: [PATCH] replace SYSV shared memory with shm filesystem

[Andi Kleen]

On Mon, Jan 10, 2000 at 01:20:40PM +0100, Christoph Rohland wrote:
> Hi folks,
> 
> This patch implements a minimal filesystem for shared memory. It
> replaces/reuses the existing SYSV shm code so you now have to mount
> the fs to be able to use SYSV SHM. But in turn we now have everything
> in place to implement posix shm. This also obsoletes vm_private_data
> in vm_area_struct.

I planed to map the Unix Sockets abstract name space to a file system
for some time now.  Because it would be silly to write another file
system just for that rather obscure feature, would it be possible
to use a subdirectory in your new shm filesystem? I haven't looked
at the code at all yet, and don't know if it can even deal with 
directories and special devices. Do you have objections to such 
a direction?

-Andi



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Re: [PATCH] replace SYSV shared memory with shm filesystem

[Christoph Rohland]

Andi Kleen <ak@muc.de> writes:

> On Mon, Jan 10, 2000 at 01:20:40PM +0100, Christoph Rohland wrote:
> > Hi folks,
> > 
> > This patch implements a minimal filesystem for shared memory. It
> > replaces/reuses the existing SYSV shm code so you now have to mount
> > the fs to be able to use SYSV SHM. But in turn we now have everything
> > in place to implement posix shm. This also obsoletes vm_private_data
> > in vm_area_struct.
> 
> I planed to map the Unix Sockets abstract name space to a file system
> for some time now.  Because it would be silly to write another file
> system just for that rather obscure feature, would it be possible
> to use a subdirectory in your new shm filesystem? I haven't looked
> at the code at all yet, and don't know if it can even deal with 
> directories and special devices. Do you have objections to such 
> a direction?

In the current state this is not possible. The shm fs does not support
directories and only regular files (which you can only mmap, no
read/write support).

But we could later extend the fs to support directories and special
files. The Unix Sockets could probably also use the same mechanisms
for locating the special fs like SYSV ipc does.

With these changes we also should then be able to mount the fs several
times. So we also get the chroot case fixed.

Greetings
		Christoph
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Re: [PATCH] replace SYSV shared memory with shm filesystem

[James Antill]

> Andi Kleen <ak@muc.de> writes:
> 
> > On Mon, Jan 10, 2000 at 01:20:40PM +0100, Christoph Rohland wrote:
> > > Hi folks,
> > > 
> > > This patch implements a minimal filesystem for shared memory. It
> > > replaces/reuses the existing SYSV shm code so you now have to mount
> > > the fs to be able to use SYSV SHM. But in turn we now have everything
> > > in place to implement posix shm. This also obsoletes vm_private_data
> > > in vm_area_struct.
> > 
> > I planed to map the Unix Sockets abstract name space to a file system
> > for some time now.  Because it would be silly to write another file
> > system just for that rather obscure feature, would it be possible
> > to use a subdirectory in your new shm filesystem? I haven't looked
> > at the code at all yet, and don't know if it can even deal with 
> > directories and special devices. Do you have objections to such 
> > a direction?
> 
> In the current state this is not possible. The shm fs does not support
> directories and only regular files (which you can only mmap, no
> read/write support).
> 
> But we could later extend the fs to support directories and special
> files. The Unix Sockets could probably also use the same mechanisms
> for locating the special fs like SYSV ipc does.
> 
> With these changes we also should then be able to mount the fs several
> times. So we also get the chroot case fixed.

 If the idea is to integrate the unix domain sockets at some point,
then I'd like to suggest that _both_ shm and unix domain sockets get a
subtree. Ie.

/kernfs/unix_domain_sockets/*
/kernfs/sysv_shared_memory/*

 Instead of...

/shm/unix_domain_sockets/*
/shm/* (apart from unix_domain_sockets, and maybe others)

 Obviously example names might be too long for your tastes.

 This also makes it easier to add new directories (don't say it won't
happen look at proc :).

 Indeed a possibly useful one that I can think of straight away is...

/kernfs/users/<uid>/

 Where it could store entries to inodes that no longer have a file
associated with them (Ie. like the proc/self/fd/* [1], but for each
user).

 I'm not saying you should implement the fs above, just that it's
going to hinder it (or anything like it) if you put shm in the root.

-- 
James Antill -- james@and.org
I am always an optimist, but frankly there is no hope.
   -Hosni Mubarek
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Re: [PATCH] replace SYSV shared memory with shm filesystem

[Richard Guenther]

Oh no! Not another /proc. Please do a different fs, perhaps you can
share some code with shmfs, but not the namespace!

Richard.

On 10 Jan 2000, James Antill wrote:
> > Andi Kleen <ak@muc.de> writes:
> > > On Mon, Jan 10, 2000 at 01:20:40PM +0100, Christoph Rohland wrote:
> > > > Hi folks,
> > > > 
> > > > This patch implements a minimal filesystem for shared memory. It
> > > > replaces/reuses the existing SYSV shm code so you now have to mount
> > > > the fs to be able to use SYSV SHM. But in turn we now have everything
> > > > in place to implement posix shm. This also obsoletes vm_private_data
> > > > in vm_area_struct.
> > > 
> > > I planed to map the Unix Sockets abstract name space to a file system
> > > for some time now.  Because it would be silly to write another file
> > > system just for that rather obscure feature, would it be possible
> > > to use a subdirectory in your new shm filesystem? I haven't looked
> > > at the code at all yet, and don't know if it can even deal with 
> > > directories and special devices. Do you have objections to such 
> > > a direction?
> > 
> > In the current state this is not possible. The shm fs does not support
> > directories and only regular files (which you can only mmap, no
> > read/write support).
> > 
> > But we could later extend the fs to support directories and special
> > files. The Unix Sockets could probably also use the same mechanisms
> > for locating the special fs like SYSV ipc does.
> > 
> > With these changes we also should then be able to mount the fs several
> > times. So we also get the chroot case fixed.
> 
>  If the idea is to integrate the unix domain sockets at some point,
> then I'd like to suggest that _both_ shm and unix domain sockets get a
> subtree. Ie.
> 
> /kernfs/unix_domain_sockets/*
> /kernfs/sysv_shared_memory/*
> 
>  Instead of...
> 
> /shm/unix_domain_sockets/*
> /shm/* (apart from unix_domain_sockets, and maybe others)
> 
>  Obviously example names might be too long for your tastes.
> 
>  This also makes it easier to add new directories (don't say it won't
> happen look at proc :).
> 
>  Indeed a possibly useful one that I can think of straight away is...
> 
> /kernfs/users/<uid>/
> 
>  Where it could store entries to inodes that no longer have a file
> associated with them (Ie. like the proc/self/fd/* [1], but for each
> user).
> 
>  I'm not saying you should implement the fs above, just that it's
> going to hinder it (or anything like it) if you put shm in the root.
> 
> -- 
> James Antill -- james@and.org
> I am always an optimist, but frankly there is no hope.
>    -Hosni Mubarek
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> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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> see: http://www.nl.linux.org/Linux-MM/
> 

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Re: [PATCH] replace SYSV shared memory with shm filesystem

[Christoph Rohland]

James Antill <james@and.org> writes:

>  If the idea is to integrate the unix domain sockets at some point,
> then I'd like to suggest that _both_ shm and unix domain sockets get a
> subtree. Ie.
> 
> /kernfs/unix_domain_sockets/*
> /kernfs/sysv_shared_memory/*

I think Unix Sockets should use a new instance of the fs and mount it
to a private place.

Greetings
		Christoph
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