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ovl: support multiple lower layers

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Allow "lowerdir=" option to contain multiple lower directories separated by
a colon (e.g. "lowerdir=/bin:/usr/bin").  Colon characters in filenames can
be escaped with a backslash.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This commit is contained in:
Miklos Szeredi 2014-12-13 00:59:52 +01:00
parent 53a08cb9b8
commit a78d9f0d5d
2 changed files with 95 additions and 27 deletions
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12
Documentation/filesystems/overlayfs.txt
View file

@ -159,6 +159,18 @@ overlay filesystem (though an operation on the name of the file such as
rename or unlink will of course be noticed and handled).
Multiple lower layers
---------------------
Multiple lower layers can now be given using the the colon (":") as a
separator character between the directory names. For example:
mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged
As the example shows, "upperdir=" and "workdir=" may be omitted. In that case
the overlay will be read-only.
Non-standard behavior
---------------------

110
fs/overlayfs/super.c
View file

@ -60,6 +60,8 @@ struct ovl_entry {
struct path lowerstack[];
};
#define OVL_MAX_STACK 500
const char *ovl_opaque_xattr = "trusted.overlay.opaque";
static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
@ -692,8 +694,12 @@ static bool ovl_is_allowed_fs_type(struct dentry *root)
static int ovl_mount_dir_noesc(const char *name, struct path *path)
{
int err;
int err = -EINVAL;
if (!*name) {
pr_err("overlayfs: empty lowerdir\n");
goto out;
}
err = kern_path(name, LOOKUP_FOLLOW, path);
if (err) {
pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
@ -735,7 +741,7 @@ static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
int err;
struct kstatfs statfs;
err = ovl_mount_dir(name, path);
err = ovl_mount_dir_noesc(name, path);
if (err)
goto out;
@ -767,15 +773,38 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
return ok;
}
static unsigned int ovl_split_lowerdirs(char *str)
{
unsigned int ctr = 1;
char *s, *d;
for (s = d = str;; s++, d++) {
if (*s == '\\') {
s++;
} else if (*s == ':') {
*d = '\0';
ctr++;
continue;
}
*d = *s;
if (!*s)
break;
}
return ctr;
}
static int ovl_fill_super(struct super_block *sb, void *data, int silent)
{
struct path lowerpath;
struct path upperpath = { NULL, NULL };
struct path workpath = { NULL, NULL };
struct dentry *root_dentry;
struct ovl_entry *oe;
struct ovl_fs *ufs;
struct vfsmount *mnt;
struct path *stack = NULL;
char *lowertmp;
char *lower;
unsigned int numlower;
unsigned int stacklen = 0;
unsigned int i;
int err;
@ -820,12 +849,30 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
}
sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
}
err = ovl_lower_dir(ufs->config.lowerdir, &lowerpath,
&ufs->lower_namelen, &sb->s_stack_depth);
if (err)
err = -ENOMEM;
lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
if (!lowertmp)
goto out_put_workpath;
err = -EINVAL;
stacklen = ovl_split_lowerdirs(lowertmp);
if (stacklen > OVL_MAX_STACK)
goto out_free_lowertmp;
stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
if (!stack)
goto out_free_lowertmp;
lower = lowertmp;
for (numlower = 0; numlower < stacklen; numlower++) {
err = ovl_lower_dir(lower, &stack[numlower],
&ufs->lower_namelen, &sb->s_stack_depth);
if (err)
goto out_put_lowerpath;
lower = strchr(lower, '\0') + 1;
}
err = -EINVAL;
sb->s_stack_depth++;
if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
@ -850,24 +897,25 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
}
}
ufs->lower_mnt = kcalloc(1, sizeof(struct vfsmount *), GFP_KERNEL);
ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
if (ufs->lower_mnt == NULL)
goto out_put_workdir;
for (i = 0; i < numlower; i++) {
struct vfsmount *mnt = clone_private_mount(&stack[i]);
mnt = clone_private_mount(&lowerpath);
err = PTR_ERR(mnt);
if (IS_ERR(mnt)) {
pr_err("overlayfs: failed to clone lowerpath\n");
goto out_put_lower_mnt;
if (IS_ERR(mnt)) {
pr_err("overlayfs: failed to clone lowerpath\n");
goto out_put_lower_mnt;
}
/*
* Make lower_mnt R/O. That way fchmod/fchown on lower file
* will fail instead of modifying lower fs.
*/
mnt->mnt_flags |= MNT_READONLY;
ufs->lower_mnt[ufs->numlower] = mnt;
ufs->numlower++;
}
/*
* Make lower_mnt R/O. That way fchmod/fchown on lower file
* will fail instead of modifying lower fs.
*/
mnt->mnt_flags |= MNT_READONLY;
ufs->lower_mnt[0] = mnt;
ufs->numlower = 1;
/* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */
if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
@ -876,7 +924,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
sb->s_d_op = &ovl_dentry_operations;
err = -ENOMEM;
oe = ovl_alloc_entry(1);
oe = ovl_alloc_entry(numlower);
if (!oe)
goto out_put_lower_mnt;
@ -885,12 +933,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
goto out_free_oe;
mntput(upperpath.mnt);
mntput(lowerpath.mnt);
for (i = 0; i < numlower; i++)
mntput(stack[i].mnt);
path_put(&workpath);
kfree(lowertmp);
oe->__upperdentry = upperpath.dentry;
oe->lowerstack[0].dentry = lowerpath.dentry;
oe->lowerstack[0].mnt = ufs->lower_mnt[0];
for (i = 0; i < numlower; i++) {
oe->lowerstack[i].dentry = stack[i].dentry;
oe->lowerstack[i].mnt = ufs->lower_mnt[i];
}
root_dentry->d_fsdata = oe;
@ -912,7 +964,11 @@ out_put_workdir:
out_put_upper_mnt:
mntput(ufs->upper_mnt);
out_put_lowerpath:
path_put(&lowerpath);
for (i = 0; i < numlower; i++)
path_put(&stack[i]);
kfree(stack);
out_free_lowertmp:
kfree(lowertmp);
out_put_workpath:
path_put(&workpath);
out_put_upperpath: