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SubjectRe: [RFC PATCH 1/2] vfs: pass file down when getattr to avoid losing info.
Jianyong Wu wrote on Mon, Jul 20, 2020:
> Currently, getting attribute for a file represented by fd is always
> by inode or path which may lead to bug for a certain network file system.
> Adding file struct into struct kstat and assigning file for it in
> vfs_statx_fd can avoid this issue. This change refers to struct istat.
>
> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> ---
> fs/stat.c | 1 +
> include/linux/stat.h | 6 ++++++
> 2 files changed, 7 insertions(+)
>
> diff --git a/fs/stat.c b/fs/stat.c
> index 44f8ad346db4..0dee5487f6d6 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> @@ -147,6 +147,7 @@ int vfs_statx_fd(unsigned int fd, struct kstat *stat,
> return -EINVAL;
>
> f = fdget_raw(fd);
> + stat->filp = f.file;
> if (f.file) {
> error = vfs_getattr(&f.file->f_path, stat,
> request_mask, query_flags);
> diff --git a/include/linux/stat.h b/include/linux/stat.h
> index 56614af83d4a..4755c528d49a 100644
> --- a/include/linux/stat.h
> +++ b/include/linux/stat.h
> @@ -48,6 +48,12 @@ struct kstat {
> struct timespec64 btime; /* File creation time */
> u64 blocks;
> u64 mnt_id;
> +
> + /*
> + * Not an attribute, but an auxiliary info for filesystems wanting to
> + * implement an fstat() like method.
> + */
> + struct file *filp;

Just, no ; don't touch this, it isn't likely to get accepted ever.
file operations should all have a filp around already, we need to fix
this in our code.

(also missing quite a few Cc if you ever want to touch these bits, at
least linux-fsdevel@)



FWIW the problem has been discussed a few times previously.

I'd appreciate if you could take over from Eric and Greg's old series
that intended to fix that:
https://lore.kernel.org/lkml/146659832556.15781.17414806975641516683.stgit@bahia.lan/

it introduced a race somewhere, but the idea looked good at the time so
it's worth looking into.

--
Dominique

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