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ovl: add mutli-layer infrastructure
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Add multiple lower layers to 'struct ovl_fs' and 'struct ovl_entry'.

ovl_entry will have an array of paths, instead of just the dentry.  This
allows a compact array containing just the layers which exist at current
point in the tree (which is expected to be a small number for the majority
of dentries).

The number of layers is not limited by this infrastructure.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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Miklos Szeredi committed Dec 12, 2014
1 parent 263b4a0 commit dd66266
Showing 1 changed file with 64 additions and 34 deletions.
98 changes: 64 additions & 34 deletions fs/overlayfs/super.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,8 @@ struct ovl_config {
/* private information held for overlayfs's superblock */
struct ovl_fs {
struct vfsmount *upper_mnt;
struct vfsmount *lower_mnt;
unsigned numlower;
struct vfsmount **lower_mnt;
struct dentry *workdir;
long lower_namelen;
/* pathnames of lower and upper dirs, for show_options */
Expand All @@ -47,7 +48,6 @@ struct ovl_dir_cache;
/* private information held for every overlayfs dentry */
struct ovl_entry {
struct dentry *__upperdentry;
struct dentry *lowerdentry;
struct ovl_dir_cache *cache;
union {
struct {
Expand All @@ -56,10 +56,16 @@ struct ovl_entry {
};
struct rcu_head rcu;
};
unsigned numlower;
struct path lowerstack[];
};

const char *ovl_opaque_xattr = "trusted.overlay.opaque";

static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
{
return oe->numlower ? oe->lowerstack[0].dentry : NULL;
}

enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
Expand All @@ -69,7 +75,7 @@ enum ovl_path_type ovl_path_type(struct dentry *dentry)
if (oe->__upperdentry) {
type = __OVL_PATH_UPPER;

if (oe->lowerdentry) {
if (oe->numlower) {
if (S_ISDIR(dentry->d_inode->i_mode))
type |= __OVL_PATH_MERGE;
} else if (!oe->opaque) {
Expand Down Expand Up @@ -117,7 +123,7 @@ struct dentry *ovl_dentry_lower(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;

return oe->lowerdentry;
return __ovl_dentry_lower(oe);
}

struct dentry *ovl_dentry_real(struct dentry *dentry)
Expand All @@ -127,7 +133,7 @@ struct dentry *ovl_dentry_real(struct dentry *dentry)

realdentry = ovl_upperdentry_dereference(oe);
if (!realdentry)
realdentry = oe->lowerdentry;
realdentry = __ovl_dentry_lower(oe);

return realdentry;
}
Expand All @@ -140,7 +146,7 @@ struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
if (realdentry) {
*is_upper = true;
} else {
realdentry = oe->lowerdentry;
realdentry = __ovl_dentry_lower(oe);
*is_upper = false;
}
return realdentry;
Expand All @@ -162,11 +168,9 @@ void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)

void ovl_path_lower(struct dentry *dentry, struct path *path)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
struct ovl_entry *oe = dentry->d_fsdata;

path->mnt = ofs->lower_mnt;
path->dentry = oe->lowerdentry;
*path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
}

int ovl_want_write(struct dentry *dentry)
Expand Down Expand Up @@ -258,8 +262,11 @@ static void ovl_dentry_release(struct dentry *dentry)
struct ovl_entry *oe = dentry->d_fsdata;

if (oe) {
unsigned int i;

dput(oe->__upperdentry);
dput(oe->lowerdentry);
for (i = 0; i < oe->numlower; i++)
dput(oe->lowerstack[i].dentry);
kfree_rcu(oe, rcu);
}
}
Expand All @@ -268,9 +275,15 @@ static const struct dentry_operations ovl_dentry_operations = {
.d_release = ovl_dentry_release,
};

static struct ovl_entry *ovl_alloc_entry(void)
static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
{
return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);

if (oe)
oe->numlower = numlower;

return oe;
}

static inline struct dentry *ovl_lookup_real(struct dentry *dir,
Expand All @@ -297,27 +310,27 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
{
struct ovl_entry *oe;
struct dentry *upperdir;
struct dentry *lowerdir;
struct path lowerdir;
struct dentry *upperdentry = NULL;
struct dentry *lowerdentry = NULL;
struct inode *inode = NULL;
int err;

err = -ENOMEM;
oe = ovl_alloc_entry();
oe = ovl_alloc_entry(1);
if (!oe)
goto out;

upperdir = ovl_dentry_upper(dentry->d_parent);
lowerdir = ovl_dentry_lower(dentry->d_parent);
ovl_path_lower(dentry->d_parent, &lowerdir);

if (upperdir) {
upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
err = PTR_ERR(upperdentry);
if (IS_ERR(upperdentry))
goto out_put_dir;

if (lowerdir && upperdentry) {
if (lowerdir.dentry && upperdentry) {
if (ovl_is_whiteout(upperdentry)) {
dput(upperdentry);
upperdentry = NULL;
Expand All @@ -327,8 +340,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
}
}
}
if (lowerdir && !oe->opaque) {
lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
if (lowerdir.dentry && !oe->opaque) {
lowerdentry = ovl_lookup_real(lowerdir.dentry, &dentry->d_name);
err = PTR_ERR(lowerdentry);
if (IS_ERR(lowerdentry))
goto out_dput_upper;
Expand All @@ -355,8 +368,12 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
}

oe->__upperdentry = upperdentry;
oe->lowerdentry = lowerdentry;

if (lowerdentry) {
oe->lowerstack[0].dentry = lowerdentry;
oe->lowerstack[0].mnt = lowerdir.mnt;
} else {
oe->numlower = 0;
}
dentry->d_fsdata = oe;
d_add(dentry, inode);

Expand All @@ -380,10 +397,12 @@ struct file *ovl_path_open(struct path *path, int flags)
static void ovl_put_super(struct super_block *sb)
{
struct ovl_fs *ufs = sb->s_fs_info;
unsigned i;

dput(ufs->workdir);
mntput(ufs->upper_mnt);
mntput(ufs->lower_mnt);
for (i = 0; i < ufs->numlower; i++)
mntput(ufs->lower_mnt[i]);

kfree(ufs->config.lowerdir);
kfree(ufs->config.upperdir);
Expand Down Expand Up @@ -641,6 +660,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
struct ovl_entry *oe;
struct ovl_fs *ufs;
struct kstatfs statfs;
struct vfsmount *mnt;
unsigned int i;
int err;

err = -ENOMEM;
Expand All @@ -661,7 +682,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
}

err = -ENOMEM;
oe = ovl_alloc_entry();
oe = ovl_alloc_entry(1);
if (oe == NULL)
goto out_free_config;

Expand Down Expand Up @@ -727,12 +748,24 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
goto out_put_workpath;
}

ufs->lower_mnt = clone_private_mount(&lowerpath);
err = PTR_ERR(ufs->lower_mnt);
if (IS_ERR(ufs->lower_mnt)) {
pr_err("overlayfs: failed to clone lowerpath\n");
ufs->lower_mnt = kcalloc(1, sizeof(struct vfsmount *), GFP_KERNEL);
if (ufs->lower_mnt == NULL)
goto out_put_upper_mnt;

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;
}
/*
* 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;

ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
err = PTR_ERR(ufs->workdir);
Expand All @@ -742,12 +775,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
goto out_put_lower_mnt;
}

/*
* Make lower_mnt R/O. That way fchmod/fchown on lower file
* will fail instead of modifying lower fs.
*/
ufs->lower_mnt->mnt_flags |= MNT_READONLY;

/* If the upper fs is r/o, we mark overlayfs r/o too */
if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
sb->s_flags |= MS_RDONLY;
Expand All @@ -768,7 +795,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
path_put(&workpath);

oe->__upperdentry = upperpath.dentry;
oe->lowerdentry = lowerpath.dentry;
oe->lowerstack[0].dentry = lowerpath.dentry;
oe->lowerstack[0].mnt = ufs->lower_mnt[0];

root_dentry->d_fsdata = oe;

Expand All @@ -782,7 +810,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
out_put_workdir:
dput(ufs->workdir);
out_put_lower_mnt:
mntput(ufs->lower_mnt);
for (i = 0; i < ufs->numlower; i++)
mntput(ufs->lower_mnt[i]);
kfree(ufs->lower_mnt);
out_put_upper_mnt:
mntput(ufs->upper_mnt);
out_put_workpath:
Expand Down

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