From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40351) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fxtCm-0007L8-Ms for qemu-devel@nongnu.org; Thu, 06 Sep 2018 08:16:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fxsxz-0001oH-NK for qemu-devel@nongnu.org; Thu, 06 Sep 2018 08:00:58 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:48008 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fxsxw-0001ZH-SZ for qemu-devel@nongnu.org; Thu, 06 Sep 2018 08:00:53 -0400 Date: Thu, 6 Sep 2018 14:00:49 +0200 From: Igor Mammedov Message-ID: <20180906140049.0d041b83@redhat.com> In-Reply-To: <914f169f-946d-901f-008e-f426183b9119@redhat.com> References: <1535630903-146863-1-git-send-email-imammedo@redhat.com> <38b3347b-8923-26e9-82a4-f69002262767@redhat.com> <20180906114945.1acd0b8e@redhat.com> <20180906125054.764d3baa@redhat.com> <914f169f-946d-901f-008e-f426183b9119@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qga: ignore non present cpus when handling qmp_guest_get_vcpus() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laszlo Ersek Cc: mdroth@linux.vnet.ibm.com, Drew Jones , qemu-devel@nongnu.org On Thu, 6 Sep 2018 13:52:49 +0200 Laszlo Ersek wrote: > On 09/06/18 12:50, Igor Mammedov wrote: > > On Thu, 6 Sep 2018 12:26:12 +0200 > > Laszlo Ersek wrote: > > > >> On 09/06/18 11:49, Igor Mammedov wrote: > >>> On Thu, 30 Aug 2018 17:51:13 +0200 > >>> Laszlo Ersek wrote: > >>> > >>>> +Drew > >>>> > >>>> On 08/30/18 14:08, Igor Mammedov wrote: > >>>>> If VM has VCPUs plugged sparselly (for example a VM started with > >>>>> 3 VCPUs (cpu0, cpu1 and cpu2) and then cpu1 was hotunplugged so > >>>>> only cpu0 and cpu2 are present), QGA will rise a error > >>>>> error: internal error: unable to execute QEMU agent command 'guest-get-vcpus': > >>>>> open("/sys/devices/system/cpu/cpu1/"): No such file or directory > >>>>> when > >>>>> virsh vcpucount FOO --guest > >>>>> is executed. > >>>>> Fix it by ignoring non present CPUs when fetching CPUs status from sysfs. > >>>>> > >>>>> Signed-off-by: Igor Mammedov > >>>>> --- > >>>>> qga/commands-posix.c | 4 +++- > >>>>> 1 file changed, 3 insertions(+), 1 deletion(-) > >>>>> > >>>>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c > >>>>> index 37e8a2d..2929872 100644 > >>>>> --- a/qga/commands-posix.c > >>>>> +++ b/qga/commands-posix.c > >>>>> @@ -2044,7 +2044,9 @@ static void transfer_vcpu(GuestLogicalProcessor *vcpu, bool sys2vcpu, > >>>>> vcpu->logical_id); > >>>>> dirfd = open(dirpath, O_RDONLY | O_DIRECTORY); > >>>>> if (dirfd == -1) { > >>>>> - error_setg_errno(errp, errno, "open(\"%s\")", dirpath); > >>>>> + if (!(sys2vcpu && errno == ENOENT)) { > >>>>> + error_setg_errno(errp, errno, "open(\"%s\")", dirpath); > >>>>> + } > >>>>> } else { > >>>>> static const char fn[] = "online"; > >>>>> int fd; > >>>>> > >>> [...] > >>> > >>>> I wonder if, instead of this patch, we should rework > >>>> qmp_guest_get_vcpus(), to silently skip processors for which this > >>>> dirpath ENOENT condition arises (i.e., return a shorter list of > >>>> GuestLogicalProcessor objects). > >>> would something like this on top of this patch do? > >>> > >>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c > >>> index 2929872..990bb80 100644 > >>> --- a/qga/commands-posix.c > >>> +++ b/qga/commands-posix.c > >>> @@ -2114,12 +2114,14 @@ GuestLogicalProcessorList *qmp_guest_get_vcpus(Error **errp) > >>> vcpu->logical_id = current++; > >>> vcpu->has_can_offline = true; /* lolspeak ftw */ > >>> transfer_vcpu(vcpu, true, &local_err); > >>> - > >>> - entry = g_malloc0(sizeof *entry); > >>> - entry->value = vcpu; > >>> - > >>> - *link = entry; > >>> - link = &entry->next; > >>> + if (errno == ENOENT) { > >>> + g_free(vcpu); > >>> + } else { > >>> + entry = g_malloc0(sizeof *entry); > >>> + entry->value = vcpu; > >>> + *link = entry; > >>> + link = &entry->next; > >>> + } > >>> } > >>> > >>> if (local_err == NULL) { > >>> > >>> [...] > >>> > >> > >> To me that looks like the right approach, but the details should be > >> polished a bit: > >> > >> - After we drop the vcpu object, "local_err" is still set, and would > >> terminate the loop in the next iteration. > > local_error is not set due 'if (!(sys2vcpu && errno == ENOENT))' > > condition in the in the transfer_vcpu(). > > ah, sorry, you did say this was on top of your original patch, but I had > forgotten the details of that. > > > the thing is that in case of vcpu2sys direction ENOENT is hard error. > > > >> - It seems like ENOENT can indeed only come from openat(), in > >> transfer_vcpu(), however, it would be nice if we could grab the error > >> code from the error object somehow, and not from the "errno" variable. I > >> vaguely recall this is what error classes were originally invented for, > >> but now we just use ERROR_CLASS_GENERIC_ERROR... > > I've checked it and errno is preserved during error_setg_errno() call but > > not saved in Error, so I've dropped that idea. > > > >> How about this: we could add a boolean output param to transfer_vcpu(), > >> called "fatal". Ignored when the function succeeds. When the function > >> fails (seen from "local_err"), the loop consults "fatal". If the error > >> is fatal, we act as before; otherwise, we drop the vcpu object, release > >> -- and zero out -- "local_err" as well, and continue. I think this is > >> more generic / safer than trying to infer the failure location from the > >> outside. > > It looked more uglier to me, so I've turned to libc style of reporting > > (assuming that g_free() doesn't touch errno ever) > > > > But if you prefer using extra parameter, I'll respin patch with it. instead of inventing not really error parameter we could move dirpath outside of transfer_vcpu(). It's bigger patch due to code movement but more straightforward logic. I'll send v2 after testing. > Michael, what is your preference? I guess I'll be fine both ways. > > Thanks, > Laszlo > > > > >> I'm not quite up to date on structured error propagation in QEMU, so > >> take the above with a grain of salt... > >> > >> Thanks, > >> Laszlo > > > >