Re: [PATCH v1 0/5] io_uring: add xattr support

[Stefan Roesch <shr@fb.com>]

On 11/29/21 5:08 PM, Clay Harris wrote:
> On Mon, Nov 29 2021 at 14:12:52 -0800, Stefan Roesch quoth thus:
> 
>> This adds the xattr support to io_uring. The intent is to have a more
>> complete support for file operations in io_uring.
>>
>> This change adds support for the following functions to io_uring:
>> - fgetxattr
>> - fsetxattr
>> - getxattr
>> - setxattr
> 
> You may wish to consider the following.
> 
> Patching for these functions makes for an excellent opportunity
> to provide a better interface.  Rather than implement fXetattr
> at all, you could enable io_uring to use functions like:
> 
> int Xetxattr(int dfd, const char *path, const char *name,
> 	[const] void *value, size_t size, int flags);
> 
> Not only does this simplify the io_uring interface down to two
> functions, but modernizes and fixes a deficit in usability.
> In terms of io_uring, this is just changing internal interfaces.
> 
> Although unnecessary for io_uring, it would be nice to at least
> consider what parts of this code could be leveraged for future
> Xetxattr2 syscalls.

Clay, 

while we can reduce the number of calls to 2, providing 4 calls will
ease the adoption of the interface. 

If you look at the userspace interface in liburing, you can see the
following function signature:

static inline void io_uring_prep_fgetxattr(struct io_uring_sqe *sqe,
		                           int         fd,
					   const char *name,
					   const char *value,
					   size_t      len)

This is very similar to what you proposed.

> 
>> Patch 1: fs: make user_path_at_empty() take a struct filename
>>   The user_path_at_empty filename parameter has been changed
>>   from a const char user pointer to a filename struct. io_uring
>>   operates on filenames.
>>   In addition also the functions that call user_path_at_empty
>>   in namei.c and stat.c have been modified for this change.
>>
>> Patch 2: fs: split off setxattr_setup function from setxattr
>>   Split off the setup part of the setxattr function
>>
>> Patch 3: fs: split off the vfs_getxattr from getxattr
>>   Split of the vfs_getxattr part from getxattr. This will
>>   allow to invoke it from io_uring.
>>
>> Patch 4: io_uring: add fsetxattr and setxattr support
>>   This adds new functions to support the fsetxattr and setxattr
>>   functions.
>>
>> Patch 5: io_uring: add fgetxattr and getxattr support
>>   This adds new functions to support the fgetxattr and getxattr
>>   functions.
>>
>>
>> There are two additional patches:
>>   liburing: Add support for xattr api's.
>>             This also includes the tests for the new code.
>>   xfstests: Add support for io_uring xattr support.
>>
>>
>> Stefan Roesch (5):
>>   fs: make user_path_at_empty() take a struct filename
>>   fs: split off setxattr_setup function from setxattr
>>   fs: split off the vfs_getxattr from getxattr
>>   io_uring: add fsetxattr and setxattr support
>>   io_uring: add fgetxattr and getxattr support
>>
>>  fs/internal.h                 |  23 +++
>>  fs/io_uring.c                 | 325 ++++++++++++++++++++++++++++++++++
>>  fs/namei.c                    |   5 +-
>>  fs/stat.c                     |   7 +-
>>  fs/xattr.c                    | 114 +++++++-----
>>  include/linux/namei.h         |   4 +-
>>  include/uapi/linux/io_uring.h |   8 +-
>>  7 files changed, 439 insertions(+), 47 deletions(-)
>>
>>
>> Signed-off-by: Stefan Roesch <shr@fb.com>
>> base-commit: c2626d30f312afc341158e07bf088f5a23b4eeeb
>> -- 
>> 2.30.2