Re: [PATCH v6 0/6] fs: introduce file_getattr and file_setattr syscalls

[Christian Brauner]

On Mon, Jun 30, 2025 at 06:20:10PM +0200, Andrey Albershteyn wrote:
> This patchset introduced two new syscalls file_getattr() and
> file_setattr(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> except they use *at() semantics. Therefore, there's no need to open the
> file to get a fd.
> 
> These syscalls allow userspace to set filesystem inode attributes on
> special files. One of the usage examples is XFS quota projects.
> 
> XFS has project quotas which could be attached to a directory. All
> new inodes in these directories inherit project ID set on parent
> directory.
> 
> The project is created from userspace by opening and calling
> FS_IOC_FSSETXATTR on each inode. This is not possible for special
> files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> with empty project ID. Those inodes then are not shown in the quota
> accounting but still exist in the directory. This is not critical but in
> the case when special files are created in the directory with already
> existing project quota, these new inodes inherit extended attributes.
> This creates a mix of special files with and without attributes.
> Moreover, special files with attributes don't have a possibility to
> become clear or change the attributes. This, in turn, prevents userspace
> from re-creating quota project on these existing files.

Only small nits I'm going to comment on that I can fix myself.
Otherwise looks great.