linux-kernel - Re: Add fchmodat2() - or add a more general syscall?

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Date:   Tue, 25 Jul 2023 19:39:51 +0100
From:   David Howells <dhowells@...hat.com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     dhowells@...hat.com, Alexey Gladkov <legion@...nel.org>,
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Subject: Re: Add fchmodat2() - or add a more general syscall?

Florian Weimer <fweimer@...hat.com> wrote:

> > Rather than adding a fchmodat2() syscall, should we add a
> > "set_file_attrs()" syscall that takes a mask and allows you to set a bunch
> > of stuff all in one go?  Basically, an interface to notify_change() in the
> > kernel that would allow several stats to be set atomically.  This might be
> > of particular interest to network filesystems.
> 
> Do you mean atomically as in compare-and-swap (update only if old values
> match), or just a way to update multiple file attributes with a single
> system call?

I was thinking more in terms of the latter.  AFAIK, there aren't any network
filesystems support a CAS interface on file attributes like that.  To be able
to do a CAS operation, we'd need to pass in the old values as well as the new.

Another thing we could look at is doing "create_and_set_attrs()", possibly
allowing it to take a list of xattrs also.

David