[RFC PATCH v3 02/10] mm/mshare: pre-populate msharefs with information file

[Anthony Yznaga <anthony.yznaga@oracle.com>]

From: Khalid Aziz <khalid@kernel.org>

Users of mshare feature to share page tables need to know the size
and alignment requirement for shared regions. Pre-populate msharefs
with a file, mshare_info, that provides this information.

Signed-off-by: Khalid Aziz <khalid@kernel.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 mm/mshare.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 73 insertions(+), 2 deletions(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index d5d8e2530e5a..6562000545e1 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -17,19 +17,73 @@
 #include <linux/fs_context.h>
 #include <uapi/linux/magic.h>
 
+struct msharefs_info {
+	struct dentry *info_dentry;
+};
+
 static const struct file_operations msharefs_file_operations = {
 	.open		= simple_open,
 	.llseek		= no_llseek,
 };
 
+static ssize_t
+mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
+		loff_t *ppos)
+{
+	char s[80];
+
+	sprintf(s, "%ld\n", PGDIR_SIZE);
+	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
+}
+
+static const struct file_operations mshare_info_ops = {
+	.read	= mshare_info_read,
+	.llseek	= noop_llseek,
+};
+
 static const struct super_operations mshare_s_ops = {
 	.statfs		= simple_statfs,
 };
 
+static int
+msharefs_create_mshare_info(struct super_block *sb)
+{
+	struct msharefs_info *info = sb->s_fs_info;
+	struct dentry *root = sb->s_root;
+	struct dentry *dentry;
+	struct inode *inode;
+	int ret;
+
+	ret = -ENOMEM;
+	inode = new_inode(sb);
+	if (!inode)
+		goto out;
+
+	inode->i_ino = 2;
+	simple_inode_init_ts(inode);
+	inode_init_owner(&nop_mnt_idmap, inode, NULL, S_IFREG | 0444);
+	inode->i_fop = &mshare_info_ops;
+
+	dentry = d_alloc_name(root, "mshare_info");
+	if (!dentry)
+		goto out;
+
+	info->info_dentry = dentry;
+	d_add(dentry, inode);
+
+	return 0;
+out:
+	iput(inode);
+
+	return ret;
+}
+
 static int
 msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
+	struct msharefs_info *info;
 	struct inode *inode;
+	int ret;
 
 	sb->s_blocksize		= PAGE_SIZE;
 	sb->s_blocksize_bits	= PAGE_SHIFT;
@@ -37,6 +91,12 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_op		= &mshare_s_ops;
 	sb->s_time_gran		= 1;
 
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	sb->s_fs_info = info;
+
 	inode = new_inode(sb);
 	if (!inode)
 		return -ENOMEM;
@@ -52,7 +112,9 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (!sb->s_root)
 		return -ENOMEM;
 
-	return 0;
+	ret = msharefs_create_mshare_info(sb);
+
+	return ret;
 }
 
 static int
@@ -72,10 +134,19 @@ mshare_init_fs_context(struct fs_context *fc)
 	return 0;
 }
 
+static void
+msharefs_kill_super(struct super_block *sb)
+{
+	struct msharefs_info *info = sb->s_fs_info;
+
+	kfree(info);
+	kill_litter_super(sb);
+}
+
 static struct file_system_type mshare_fs = {
 	.name			= "msharefs",
 	.init_fs_context	= mshare_init_fs_context,
-	.kill_sb		= kill_litter_super,
+	.kill_sb		= msharefs_kill_super,
 };
 
 static int __init
-- 
2.43.5