[PATCH v3] fs: introduce getfsxattrat and setfsxattrat syscalls

[Arnd Bergmann]

On Tue, Feb 11, 2025, at 18:22, Andrey Albershteyn wrote:
> From: Andrey Albershteyn <aalbersh at redhat.com>
>
> Introduce getfsxattrat and setfsxattrat syscalls to manipulate inode
> extended attributes/flags. The syscalls take parent directory fd and
> path to the child together with struct fsxattr.
>
> This is an alternative to FS_IOC_FSSETXATTR ioctl with a difference
> that file don't need to be open as we can reference it with a path
> instead of fd. By having this we can manipulated inode extended
> attributes not only on regular files but also on special ones. This
> is not possible with FS_IOC_FSSETXATTR ioctl as with special files
> we can not call ioctl() directly on the filesystem inode using fd.
>
> This patch adds two new syscalls which allows userspace to get/set
> extended inode attributes on special files by using parent directory
> and a path - *at() like syscall.
>
> Also, as vfs_fileattr_set() is now will be called on special files
> too, let's forbid any other attributes except projid and nextents
> (symlink can have an extent).
>
> CC: linux-api at vger.kernel.org
> CC: linux-fsdevel at vger.kernel.org
> CC: linux-xfs at vger.kernel.org
> Signed-off-by: Andrey Albershteyn <aalbersh at redhat.com>

I checked the syscall.tbl additions and the ABI to ensure that
it follows the usual guidelines and is portable across
all architectures, this looks good. Thanks for addressing
my v1 comments:

Acked-by: Arnd Bergmann <arnd at arndb.de>

Disclaimer: I have no idea if the new syscalls are a good
idea or if they are fit for the purpose, I trust the
VFS maintainers will take care of reviewing that.