On Fri, Jun 23, 2017 at 1:01 PM, Chandan Rajendra
<chandan@xxxxxxxxxxxxxxxxxx> wrote:
> For stat(2) on lowerdir non-dir entries in non-samefs case, this commit
> provides unique values for st_dev. The unique values are obtained by
> allocating anonymous bdevs for each of the lowerdirs in the overlayfs
> instance.
>
> Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
> ---
> Changelog:
> v1->v2: Drop code that provided unique st_dev across copy up.
>
> fs/overlayfs/inode.c | 20 ++++++++++++++++++++
> fs/overlayfs/ovl_entry.h | 8 +++++++-
> fs/overlayfs/super.c | 33 +++++++++++++++++++++++++--------
> 3 files changed, 52 insertions(+), 9 deletions(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index d613e2c..e30bdca 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -8,11 +8,29 @@
> */
>
> #include <linux/fs.h>
> +#include <linux/mount.h>
> #include <linux/slab.h>
> #include <linux/cred.h>
> #include <linux/xattr.h>
> #include <linux/posix_acl.h>
> #include "overlayfs.h"
> +#include "ovl_entry.h"
> +
> +static dev_t ovl_get_pseudo_dev(struct dentry *dentry, dev_t dev)
> +{
> + struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> + int i;
> +
> + if (ofs->upper_mnt && ofs->upper_mnt->mnt_sb->s_dev == dev)
> + return dev;
> +
> + for (i = 0; i < ofs->numlower; i++) {
> + if (ofs->lower_mnt[i].real_dev == dev)
> + return ofs->lower_mnt[i].pseudo_dev;
> + }
> +
> + return dev;
> +}
This is a good way to test out the functionality. But there's a
trivial way to optimize away the O(num of layers) from this function:
instead of using struct path for lower stack, use
struct ovl_lower {
struct ovl_lower_mnt *layer;
struct dentry *dentry;
};
That means one more dereference to get the vfsmount, but I don't think
we need to care about that.
>
> int ovl_setattr(struct dentry *dentry, struct iattr *attr)
> {
> @@ -116,6 +134,8 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
> */
> stat->dev = dentry->d_sb->s_dev;
> stat->ino = dentry->d_inode->i_ino;
> + } else {
> + stat->dev = ovl_get_pseudo_dev(dentry, stat->dev);
> }
>
> /*
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 34bc4a9..92aebe9 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -16,11 +16,17 @@ struct ovl_config {
> bool redirect_dir;
> };
>
> +struct ovl_lower_mnt {
> + struct vfsmount *mnt;
> + dev_t real_dev;
Why store the real_dev? It's stored in mnt->mnt_sb->s_dev, right?
> + dev_t pseudo_dev;
> +};
> +
> /* private information held for overlayfs's superblock */
> struct ovl_fs {
> struct vfsmount *upper_mnt;
> unsigned numlower;
> - struct vfsmount **lower_mnt;
> + struct ovl_lower_mnt *lower_mnt;
> struct dentry *workdir;
> long namelen;
> /* pathnames of lower and upper dirs, for show_options */
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 4882ffb..c922a92 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -172,8 +172,10 @@ static void ovl_put_super(struct super_block *sb)
>
> dput(ufs->workdir);
> mntput(ufs->upper_mnt);
> - for (i = 0; i < ufs->numlower; i++)
> - mntput(ufs->lower_mnt[i]);
> + for (i = 0; i < ufs->numlower; i++) {
> + mntput(ufs->lower_mnt[i].mnt);
> + free_anon_bdev(ufs->lower_mnt[i].pseudo_dev);
> + }
> kfree(ufs->lower_mnt);
>
> kfree(ufs->config.lowerdir);
> @@ -908,15 +910,25 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> }
>
> err = -ENOMEM;
> - ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
> + ufs->lower_mnt = kcalloc(numlower, sizeof(struct ovl_lower_mnt),
> + 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]);
> + struct vfsmount *mnt;
> + dev_t dev;
>
> + err = get_anon_bdev(&dev);
> + if (err) {
> + pr_err("overlayfs: failed to get anonymous bdev for lowerpath\n");
> + goto out_put_lower_mnt;
> + }
> +
> + mnt = clone_private_mount(&stack[i]);
> err = PTR_ERR(mnt);
> if (IS_ERR(mnt)) {
> pr_err("overlayfs: failed to clone lowerpath\n");
> + free_anon_bdev(dev);
> goto out_put_lower_mnt;
> }
> /*
> @@ -925,7 +937,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> */
> mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
>
> - ufs->lower_mnt[ufs->numlower] = mnt;
> + ufs->lower_mnt[ufs->numlower].mnt = mnt;
> + ufs->lower_mnt[ufs->numlower].real_dev = mnt->mnt_sb->s_dev;
> + ufs->lower_mnt[ufs->numlower].pseudo_dev = dev;
> ufs->numlower++;
>
> /* Check if all lower layers are on same sb */
> @@ -980,7 +994,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> }
> for (i = 0; i < numlower; i++) {
> oe->lowerstack[i].dentry = stack[i].dentry;
> - oe->lowerstack[i].mnt = ufs->lower_mnt[i];
> + oe->lowerstack[i].mnt = ufs->lower_mnt[i].mnt;
> }
> kfree(stack);
>
> @@ -999,8 +1013,11 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
> out_put_cred:
> put_cred(ufs->creator_cred);
> out_put_lower_mnt:
> - for (i = 0; i < ufs->numlower; i++)
> - mntput(ufs->lower_mnt[i]);
> + for (i = 0; i < ufs->numlower; i++) {
> + if (ufs->lower_mnt[i].mnt)
> + free_anon_bdev(ufs->lower_mnt[i].pseudo_dev);
> + mntput(ufs->lower_mnt[i].mnt);
> + }
> kfree(ufs->lower_mnt);
> out_put_workdir:
> dput(ufs->workdir);
> --
> 2.9.4
>
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