Received: from eggs.gnu.org ([2001:4830:134:3::10]:36586) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gCkcF-0004I2-Qa for qemu-devel@nongnu.org; Wed, 17 Oct 2018 08:07:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gCkcE-0006vC-Tq for qemu-devel@nongnu.org; Wed, 17 Oct 2018 08:07:55 -0400 From: Juan Quintela In-Reply-To: <20181016140655.GI2426@work-vm> (David Alan Gilbert's message of "Tue, 16 Oct 2018 15:06:55 +0100") References: <20181010203735.27918-1-aclindsa@gmail.com> <20181010203735.27918-4-aclindsa@gmail.com> <3a964ae2-a5d0-5960-9e15-7ede929a8294@linaro.org> <20181016082117.GB2426@work-vm> <20181016135517.GO3671@okra.localdomain> <20181016140655.GI2426@work-vm> Reply-To: quintela@redhat.com Date: Wed, 17 Oct 2018 14:07:32 +0200 Message-ID: <87y3aw93p7.fsf@trasno.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v6 03/14] migration: Add post_save function to VMStateDescription List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert" Cc: Aaron Lindsay , Richard Henderson , Wei Huang , Peter Maydell , Michael Spradling , Digant Desai , Peter Crosthwaite , qemu-devel@nongnu.org, Alistair Francis , qemu-arm@nongnu.org "Dr. David Alan Gilbert" wrote: > * Aaron Lindsay (aclindsa@gmail.com) wrote: >> On Oct 16 09:21, Dr. David Alan Gilbert wrote: >> > * Richard Henderson (richard.henderson@linaro.org) wrote: >> > > On 10/10/18 1:37 PM, Aaron Lindsay wrote: >> > > > In some cases it may be helpful to modify state before saving it for >> > > > migration, and then modify the state back after it has been saved. The >> > > > existing pre_save function provides half of this functionality. This >> > > > patch adds a post_save function to provide the second half. >> > > > >> > > > Signed-off-by: Aaron Lindsay >> > > > --- >> > > > docs/devel/migration.rst | 9 +++++++-- >> > > > include/migration/vmstate.h | 1 + >> > > > migration/vmstate.c | 10 +++++++++- >> > > > 3 files changed, 17 insertions(+), 3 deletions(-) >> > > >> > > Hmm, maybe. I believe the common practice is for pre_save to >> > > copy state into a >> > > separate member on the side, so that conversion back isn't necessary. >> > > >> > > Ccing in the migration maintainers for a second opinion. >> > >> > It is common to copy stuff into a separate member; however we do >> > occasionally think that post_save would be a useful addition; so I think >> > we should take it (if nothing else it actually makes stuff symmetric!). >> > >> > Please make it return 'int' in the same way that pre_save/pre_load >> > does, so that it can fail and stop the migration. >> >> This patch calls post_save *even if the save operation fails*. My >> reasoning was that I didn't want a failed migration to leave a >> still-running original QEMU instance in an invalid state. Was this >> misguided? > > That's fine - my only issue is that I want post_save to be able to fail > itself even if pre_save failed. > >> If it was not, which error do you prefer to be returned from >> vmstate_save_state_v() in the case that both the save operation itself >> and the post_save call returned errors? > > The return value from the save operation. > I did wonder about suggesting that you pass the return value from the > save operation as a parameter to post_save. The one from save. In general, this one shouldn't be called, and if it gets an error, we are really in big trouble, no? By big treauble I mean that we can basically only stop the guest? Later, Juan. > > Dave > >> -Aaron > -- > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK