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

[Clay Harris <bugs@claycon.org>]

On Wed, Dec 01 2021 at 13:19:03 +0100, Stefan Metzmacher quoth thus:

> Hi Stefan,
> 
> > 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.
> 
> What's with lsetxattr and lgetxattr, why are they missing.
Do any filesystems even support xattrs on symbolic links?

> I'd assume that even 6 helper functions in liburing would be able
> to use just 2 low level iouring opcodes.
> 
> *listxattr is also missing, are there plans for them?
> 
> metze