On Tue, Nov 25, 2025 at 08:40:07AM +0100, Markus Armbruster wrote: > g_autoptr(T) is quite useful when the object's extent matches the > function's. > > This isn't the case for an Error object the function propagates to its > caller. It is the case for an Error object the function reports or > handles itself. However, the functions to report Error also free it. > > Thus, g_autoptr(Error) is rarely applicable. We have just three > instances out of >1100 local Error variables, all in migration code. > > Two want to move the error to the MigrationState for later handling / > reporting. Since migrate_set_error() doesn't move, but stores a copy, > the original needs to be freed, and g_autoptr() is correct there. We > have 17 more that instead manually free with error_free() or > error_report_err() right after migrate_set_error(). > > We recently discussed storing a copy vs. move the original: > > From: Peter Xu <[email protected]> > Subject: Re: [PATCH 0/3] migration: Error fixes and improvements > Date: Mon, 17 Nov 2025 11:03:37 -0500 > Message-ID: <[email protected]> > > The two g_autoptr() gave me pause when I investigated this topic, simply > because they deviate from the common pattern migrate_set_error(s, err) > followed by error_free() or error_report_err(). > > The third one became wrong when I cleaned up the reporting (missed in > the cleanup patch, fixed in the patch I'm replying to). I suspect my > mistake escaped review for the same reason I made it: g_autoptr(Error) > is unusual and not visible in the patch hunk. > > Would you like me to replace the two correct uses of g_autoptr(Error) by > more common usage?
I had previously proposed g_autoptr(Error) a year or two back and you rejected it then, so I'm surprised to see that it got into the code, because it requires explicit opt-in via a G_DEFINE_AUTOPTR_CLEANUP_FUNC. Unfortunately it appears exactly that was added earlier this year in commit 18eb55546a54e443d94a4c49286348176ad4b00a Author: Maciej S. Szmigiero <[email protected]> Date: Tue Mar 4 23:03:35 2025 +0100 error: define g_autoptr() cleanup function for the Error type Automatic memory management helps avoid memory safety issues. Reviewed-by: Peter Xu <[email protected]> Signed-off-by: Maciej S. Szmigiero <[email protected]> Link: https://lore.kernel.org/qemu-devel/a5843c5fa64d7e5239a4316092ec0ef0d10c2320.1741124640.git.maciej.szmigi...@oracle.com Signed-off-by: Cédric Le Goater <[email protected]> When removing this usage, ensure that commit is reverted too, which will prevent anyone unwittingly re-introducing g_autoptr(Error) usage With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
