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Subject: [PATCH v2 2/9] mm/mshare: pre-populate msharefs with information file
Date:   Wed, 29 Jun 2022 16:53:53 -0600
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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.aziz@oracle.com>
---
 mm/mshare.c | 62 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 14 deletions(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index c8fab3869bab..3e448e11c742 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -25,8 +25,8 @@
 static struct super_block *msharefs_sb;
 
 static const struct file_operations msharefs_file_operations = {
-	.open	= simple_open,
-	.llseek	= no_llseek,
+	.open		= simple_open,
+	.llseek		= no_llseek,
 };
 
 static int
@@ -42,23 +42,52 @@ msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr)
 	return 0;
 }
 
+static void
+mshare_evict_inode(struct inode *inode)
+{
+	clear_inode(inode);
+}
+
 static const struct dentry_operations msharefs_d_ops = {
 	.d_hash = msharefs_d_hash,
 };
 
+static ssize_t
+mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
+		loff_t *ppos)
+{
+	char s[80];
+
+	sprintf(s, "%ld", 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,
+	.evict_inode = mshare_evict_inode,
+};
+
 static int
 msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
-	static const struct tree_descr empty_descr = {""};
+	static const struct tree_descr mshare_files[] = {
+		[2] = { "mshare_info", &mshare_info_ops, 0444},
+		{""},
+	};
 	int err;
 
-	sb->s_d_op = &msharefs_d_ops;
-	err = simple_fill_super(sb, MSHARE_MAGIC, &empty_descr);
-	if (err)
-		return err;
-
-	msharefs_sb = sb;
-	return 0;
+	err = simple_fill_super(sb, MSHARE_MAGIC, mshare_files);
+	if (!err) {
+		msharefs_sb = sb;
+		sb->s_d_op = &msharefs_d_ops;
+		sb->s_op = &mshare_s_ops;
+	}
+	return err;
 }
 
 static int
@@ -84,20 +113,25 @@ static struct file_system_type mshare_fs = {
 	.kill_sb		= kill_litter_super,
 };
 
-static int
+static int __init
 mshare_init(void)
 {
 	int ret = 0;
 
 	ret = sysfs_create_mount_point(fs_kobj, "mshare");
 	if (ret)
-		return ret;
+		goto out;
 
 	ret = register_filesystem(&mshare_fs);
-	if (ret)
+	if (ret) {
 		sysfs_remove_mount_point(fs_kobj, "mshare");
+		goto out;
+	}
+
+	return 0;
 
+out:
 	return ret;
 }
 
-fs_initcall(mshare_init);
+core_initcall(mshare_init);
-- 
2.32.0