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overlayfs: implement show_options 

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.

AV: even failing ovl_parse_opt() could've done some kstrdup()
AV: failure of ovl_alloc_entry() should end up with ENOMEM, not EINVAL

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This commit is contained in:
Erez Zadok 2014-10-24 00:14:38 +02:00 committed by Miklos Szeredi
parent cc2596392a
commit f45827e841
1 changed files with 48 additions and 28 deletions
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76
fs/overlayfs/super.c
View File

@ -17,6 +17,7 @@
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/statfs.h>
#include <linux/seq_file.h>
#include "overlayfs.h"
MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
@ -25,12 +26,20 @@ MODULE_LICENSE("GPL");
#define OVERLAYFS_SUPER_MAGIC 0x794c764f
struct ovl_config {
char *lowerdir;
char *upperdir;
char *workdir;
};
/* private information held for overlayfs's superblock */
struct ovl_fs {
struct vfsmount *upper_mnt;
struct vfsmount *lower_mnt;
struct dentry *workdir;
long lower_namelen;
/* pathnames of lower and upper dirs, for show_options */
struct ovl_config config;
};
struct ovl_dir_cache;
@ -384,6 +393,9 @@ 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->config.workdir);
kfree(ufs);
}
@ -413,15 +425,27 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
return err;
}
/**
* 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 dentry *dentry)
{
struct super_block *sb = dentry->d_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);
seq_printf(m, ",workdir=%s", ufs->config.workdir);
return 0;
}
static const struct super_operations ovl_super_operations = {
.put_super = ovl_put_super,
.statfs = ovl_statfs,
};
struct ovl_config {
char *lowerdir;
char *upperdir;
char *workdir;
.show_options = ovl_show_options,
};
enum {
@ -442,10 +466,6 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
{
char *p;
config->upperdir = NULL;
config->lowerdir = NULL;
config->workdir = NULL;
while ((p = strsep(&opt, ",")) != NULL) {
int token;
substring_t args[MAX_OPT_ARGS];
@ -586,39 +606,40 @@ 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;
struct kstatfs statfs;
int err;
err = ovl_parse_opt((char *) data, &config);
if (err)
err = -ENOMEM;
ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
if (!ufs)
goto out;
err = ovl_parse_opt((char *) data, &ufs->config);
if (err)
goto out_free_config;
/* FIXME: workdir is not needed for a R/O mount */
err = -EINVAL;
if (!config.upperdir || !config.lowerdir || !config.workdir) {
if (!ufs->config.upperdir || !ufs->config.lowerdir ||
!ufs->config.workdir) {
pr_err("overlayfs: missing upperdir or lowerdir or workdir\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;
err = ovl_mount_dir(config.upperdir, &upperpath);
err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
if (err)
goto out_free_oe;
err = ovl_mount_dir(config.lowerdir, &lowerpath);
err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
if (err)
goto out_put_upperpath;
err = ovl_mount_dir(config.workdir, &workpath);
err = ovl_mount_dir(ufs->config.workdir, &workpath);
if (err)
goto out_put_lowerpath;
@ -674,7 +695,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
err = PTR_ERR(ufs->workdir);
if (IS_ERR(ufs->workdir)) {
pr_err("overlayfs: failed to create directory %s/%s\n",
config.workdir, OVL_WORKDIR_NAME);
ufs->config.workdir, OVL_WORKDIR_NAME);
goto out_put_lower_mnt;
}
@ -729,12 +750,11 @@ out_put_upperpath:
path_put(&upperpath);
out_free_oe:
kfree(oe);
out_free_ufs:
kfree(ufs);
out_free_config:
kfree(config.lowerdir);
kfree(config.upperdir);
kfree(config.workdir);
kfree(ufs->config.lowerdir);
kfree(ufs->config.upperdir);
kfree(ufs->config.workdir);
kfree(ufs);
out:
return err;
}