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Subject[PATCH 6/7] overlayfs: implement show_options
Date
From: Erez Zadok <ezk@fsl.cs.sunysb.edu>

This is useful because of the stacking nature of overlayfs. Users like to
find out (via /proc/mounts) which lower/upper directory were used at mount
time.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
fs/overlayfs/super.c | 63 ++++++++++++++++++++++++++++++++++----------------
1 files changed, 43 insertions(+), 20 deletions(-)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index c9db954..7109b45 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -15,17 +15,27 @@
#include <linux/slab.h>
#include <linux/parser.h>
#include <linux/module.h>
+#include <linux/seq_file.h>
#include "overlayfs.h"

MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
MODULE_DESCRIPTION("Overlay filesystem");
MODULE_LICENSE("GPL");

+struct ovl_config {
+ char *lowerdir;
+ char *upperdir;
+};
+
+/* private information held for overlayfs's superblock */
struct ovl_fs {
struct vfsmount *upper_mnt;
struct vfsmount *lower_mnt;
+ /* pathnames of lower and upper dirs, for show_options */
+ struct ovl_config config;
};

+/* private information held for every overlayfs dentry */
struct ovl_entry {
/*
* Keep "double reference" on upper dentries, so that
@@ -363,6 +373,8 @@ static void ovl_put_super(struct super_block *sb)
mntput(ufs->upper_mnt);
mntput(ufs->lower_mnt);

+ kfree(ufs->config.lowerdir);
+ kfree(ufs->config.upperdir);
kfree(ufs);
}

@@ -404,15 +416,27 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
return path.dentry->d_sb->s_op->statfs(path.dentry, buf);
}

+/**
+ * ovl_show_options
+ *
+ * Prints the mount options for a given superblock.
+ * Returns zero; does not fail.
+ */
+static int ovl_show_options(struct seq_file *m, struct vfsmount *mnt)
+{
+ struct super_block *sb = mnt->mnt_sb;
+ struct ovl_fs *ufs = sb->s_fs_info;
+
+ seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
+ seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
+ return 0;
+}
+
static const struct super_operations ovl_super_operations = {
.put_super = ovl_put_super,
.remount_fs = ovl_remount_fs,
.statfs = ovl_statfs,
-};
-
-struct ovl_config {
- char *lowerdir;
- char *upperdir;
+ .show_options = ovl_show_options,
};

enum {
@@ -472,37 +496,36 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
struct dentry *root_dentry;
struct ovl_entry *oe;
struct ovl_fs *ufs;
- struct ovl_config config;
int err;

- err = ovl_parse_opt((char *) data, &config);
- if (err)
+ err = -ENOMEM;
+ ufs = kmalloc(sizeof(struct ovl_fs), GFP_KERNEL);
+ if (!ufs)
goto out;

+ err = ovl_parse_opt((char *) data, &ufs->config);
+ if (err)
+ goto out_free_ufs;
+
err = -EINVAL;
- if (!config.upperdir || !config.lowerdir) {
+ if (!ufs->config.upperdir || !ufs->config.lowerdir) {
printk(KERN_ERR "overlayfs: missing upperdir or lowerdir\n");
goto out_free_config;
}

- err = -ENOMEM;
- ufs = kmalloc(sizeof(struct ovl_fs), GFP_KERNEL);
- if (!ufs)
- goto out_free_config;
-
oe = ovl_alloc_entry();
if (oe == NULL)
- goto out_free_ufs;
+ goto out_free_config;

root_inode = ovl_new_inode(sb, S_IFDIR, oe);
if (!root_inode)
goto out_free_oe;

- err = kern_path(config.upperdir, LOOKUP_FOLLOW, &upperpath);
+ err = kern_path(ufs->config.upperdir, LOOKUP_FOLLOW, &upperpath);
if (err)
goto out_put_root;

- err = kern_path(config.lowerdir, LOOKUP_FOLLOW, &lowerpath);
+ err = kern_path(ufs->config.lowerdir, LOOKUP_FOLLOW, &lowerpath);
if (err)
goto out_put_upperpath;

@@ -566,11 +589,11 @@ out_put_root:
iput(root_inode);
out_free_oe:
kfree(oe);
+out_free_config:
+ kfree(ufs->config.lowerdir);
+ kfree(ufs->config.upperdir);
out_free_ufs:
kfree(ufs);
-out_free_config:
- kfree(config.lowerdir);
- kfree(config.upperdir);
out:
return err;
}
--
1.7.3.4


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