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SubjectRe: [PATCH 03/10] coda: honor AT_STATX_DONT_SYNC
On Wed, Sep 20, 2017 at 10:39:58AM +0200, Miklos Szeredi wrote:
> The description of this flag says "Don't sync attributes with the server".
> In other words: always use the attributes cached in the kernel and don't
> send network or local messages to refresh the attributes.

What is the use case for this AT_STATX_DONT_SYNC flag?

I'm asking because the Coda userspace client potentially has attributes
that are not cached in the kernel but can be (re-)validated without
network communication. So if we just care about avoiding network
traffic we could propagate the flag up to userspace. If we want to avoid
context switches, disk I/O and only check on what happens to be cached
in the kernel the current approach works fine.

Jan

> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> Cc: Jan Harkes <jaharkes@cs.cmu.edu>
> ---
> fs/coda/inode.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/coda/inode.c b/fs/coda/inode.c
> index 6058df380cc0..734672b2cbdc 100644
> --- a/fs/coda/inode.c
> +++ b/fs/coda/inode.c
> @@ -255,7 +255,10 @@ static void coda_evict_inode(struct inode *inode)
> int coda_getattr(const struct path *path, struct kstat *stat,
> u32 request_mask, unsigned int flags)
> {
> - int err = coda_revalidate_inode(d_inode(path->dentry));
> + int err = 0;
> +
> + if (!(flags & AT_STATX_DONT_SYNC))
> + err = coda_revalidate_inode(d_inode(path->dentry));
> if (!err)
> generic_fillattr(d_inode(path->dentry), stat);
> return err;
> --
> 2.5.5
>
>

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