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

[Stefan Roesch <shr@fb.com>]

On 11/29/21 7:16 PM, Andreas Dilger wrote:
> 
>> On Nov 29, 2021, at 6:08 PM, Clay Harris <bugs@claycon.org> 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);
> 
> This would naturally be named "...xattrat()"?
> 
>> 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.
> 
> Even better would be the ability to get/set an array of xattrs in
> one call, to avoid repeated path lookups in the common case of
> handling multiple xattrs on a single file.
> 

You are proposing a new API. However that API has its challenges:
- How do you implement error handling? What if only some requests fail.
- It will make the code considerably more complicated (for user-space
  as well as kernel)

Instead the user can do the following:
- io_uring already has support for the following:
  - io_uring already has the ability to prepare several SQE's at once
  - These SQE's can be submitted in one operation
  - The SQE's can also be linked and waited for as a unit.
  - Allows to map each individual CQE to its request.

>> 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.
> 
>>
>>> 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
> 
> 
> Cheers, Andreas
> 
> 
> 
> 
>