[RFC PATCH v3 04/10] mm/mshare: allocate an mm_struct for msharefs files

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

When a new file is created under msharefs, allocate a new mm_struct
to be associated with it for the lifetime of the file.
The mm_struct will hold the VMAs and pagetables for the mshare region
the file represents.

Signed-off-by: Khalid Aziz <khalid@kernel.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 mm/mshare.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/mm/mshare.c b/mm/mshare.c
index f718b8934cdf..a37849e724e1 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -17,6 +17,10 @@
 #include <linux/fs_context.h>
 #include <uapi/linux/magic.h>
 
+struct mshare_data {
+	struct mm_struct *mm;
+};
+
 struct msharefs_info {
 	struct dentry *info_dentry;
 };
@@ -29,11 +33,51 @@ static const struct file_operations msharefs_file_operations = {
 	.llseek		= no_llseek,
 };
 
+static int
+msharefs_fill_mm(struct inode *inode)
+{
+	struct mm_struct *mm;
+	struct mshare_data *m_data = NULL;
+	int ret = 0;
+
+	mm = mm_alloc();
+	if (!mm) {
+		ret = -ENOMEM;
+		goto err_free;
+	}
+
+	mm->mmap_base = mm->task_size = 0;
+
+	m_data = kzalloc(sizeof(*m_data), GFP_KERNEL);
+	if (!m_data) {
+		ret = -ENOMEM;
+		goto err_free;
+	}
+	m_data->mm = mm;
+	inode->i_private = m_data;
+
+	return 0;
+
+err_free:
+	if (mm)
+		mmput(mm);
+	kfree(m_data);
+	return ret;
+}
+
+static void
+msharefs_delmm(struct mshare_data *m_data)
+{
+	mmput(m_data->mm);
+	kfree(m_data);
+}
+
 static struct inode
 *msharefs_get_inode(struct mnt_idmap *idmap, struct super_block *sb,
 			const struct inode *dir, umode_t mode)
 {
 	struct inode *inode = new_inode(sb);
+	int ret;
 
 	if (!inode)
 		return ERR_PTR(-ENOMEM);
@@ -46,6 +90,11 @@ static struct inode
 	case S_IFREG:
 		inode->i_op = &msharefs_file_inode_ops;
 		inode->i_fop = &msharefs_file_operations;
+		ret = msharefs_fill_mm(inode);
+		if (ret) {
+			discard_new_inode(inode);
+			inode = ERR_PTR(ret);
+		}
 		break;
 	case S_IFDIR:
 		inode->i_op = &msharefs_dir_inode_ops;
@@ -141,6 +190,16 @@ static const struct inode_operations msharefs_dir_inode_ops = {
 	.rename		= msharefs_rename,
 };
 
+static void
+mshare_evict_inode(struct inode *inode)
+{
+	struct mshare_data *m_data = inode->i_private;
+
+	if (m_data)
+		msharefs_delmm(m_data);
+	clear_inode(inode);
+}
+
 static ssize_t
 mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
 		loff_t *ppos)
@@ -158,6 +217,7 @@ static const struct file_operations mshare_info_ops = {
 
 static const struct super_operations mshare_s_ops = {
 	.statfs		= simple_statfs,
+	.evict_inode	= mshare_evict_inode,
 };
 
 static int
-- 
2.43.5