On Tue, Feb 11, 2025, at 18:22, Andrey Albershteyn wrote:

From: Andrey Albershteyn <redacted>

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@vger.kernel.org
CC: linux-fsdevel@vger.kernel.org
CC: linux-xfs@vger.kernel.org
Signed-off-by: Andrey Albershteyn <redacted>

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@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.