On Friday, July 14, 2017 3:08:31 PM IST Miklos Szeredi wrote:
> 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.
>
Hi Miklos,
IIUC, 'struct ovl_entry' would then be,
/* private information held for every overlayfs dentry */
struct ovl_entry {
union {
struct {
unsigned long has_upper;
bool opaque;
};
struct rcu_head rcu;
};
unsigned numlower;
struct ovl_lower lowerstack[];
};
... ovl_path_lower() would then be having a "struct ovl_lower *" as its
second argument.
With the above listed changes, ovl_get_pseudo_dev() can then be fed a "struct
ovl_path_lower *" and hence, as you had indicated the 'for' loop can be
replaced with a statement returning the value of ovl_lower->layer->pseudo_dev.
> >
> > 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?
You are right. I will fix it up in the next version of this patch.
Thanks for your review comments.
>
> > + dev_t pseudo_dev;
> > +};
> > +
--
chandan
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