Re: [PATCH v2 0/4] io_uring: call statx directly

[Jens Axboe <axboe@kernel.dk>]

On 5/22/20 10:31 PM, Bijan Mottahedeh wrote:
> v1 -> v2
> 
> - Separate statx and open in io_kiocb 
> - Remove external declarations for unused statx interfaces
> 
> This patch set is a fix for the liburing statx test failure.
> 
> The test fails with a "Miscompare between io_uring and statx" error
> because the statx system call path has additional processing in vfs_statx():
> 
>         stat->result_mask |= STATX_MNT_ID;
>         if (path.mnt->mnt_root == path.dentry)
>                 stat->attributes |= STATX_ATTR_MOUNT_ROOT;
>         stat->attributes_mask |= STATX_ATTR_MOUNT_ROOT;
> 
> which then results in different result_mask values.
> 
> Allowing the system call to be invoked directly simplifies the io_uring
> interface and avoids potential future incompatibilities.  I'm not sure
> if there was other reasoning fort not doing so initially.
> 
> One issue I cannot account for is the difference in "used" memory reported
> by free(1) after running the statx a large (10000) number of times.
> 
> The difference is significant ~100k and doesn't really change after
> dropping caches.
> 
> I enabled memory leak detection and couldn't see anything related to the test.
> 
> Bijan Mottahedeh (4):
>   io_uring: add io_statx structure
>   statx: allow system call to be invoked from io_uring
>   io_uring: call statx directly
>   statx: hide interfaces no longer used by io_uring
> 
>  fs/internal.h |  4 ++--
>  fs/io_uring.c | 72 +++++++++++++++--------------------------------------------
>  fs/stat.c     | 37 +++++++++++++++++-------------
>  3 files changed, 42 insertions(+), 71 deletions(-)

Thanks, this looks better. For a bit of history, the initial attempt was
to do the statx without async offload if we could do so without blocking.
Without that, we may as well simplify it.

-- 
Jens Axboe