From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:57841) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SC9gY-0006HK-G5 for Qemu-devel@nongnu.org; Mon, 26 Mar 2012 09:10:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SC9gR-0000ma-TD for Qemu-devel@nongnu.org; Mon, 26 Mar 2012 09:10:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33719) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SC9gR-0000m9-LE for Qemu-devel@nongnu.org; Mon, 26 Mar 2012 09:10:03 -0400 Message-ID: <4F706B80.9080402@redhat.com> Date: Mon, 26 Mar 2012 15:13:36 +0200 From: Kevin Wolf MIME-Version: 1.0 References: <4F702B56.8030400@redhat.com> <20120326094610.2ee5abc8@doriath.home> In-Reply-To: <20120326094610.2ee5abc8@doriath.home> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Ignoring errno makes QMP errors suck List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Luiz Capitulino Cc: Qemu-devel@nongnu.org, Anthony Liguori Am 26.03.2012 14:46, schrieb Luiz Capitulino: > On Mon, 26 Mar 2012 10:39:50 +0200 > Kevin Wolf wrote: > >> Hi, >> >> I keep getting reports of problems, with nice error descriptions that >> usually look very similar to what I produced here: >> >> {"execute":"blockdev-snapshot-sync","arguments":{"device":"ide0-hd0","snapshot-file":"/tmp/backing.qcow2"}} >> {"error": {"class": "OpenFileFailed", "desc": "Could not open >> '/tmp/backing.qcow2'", "data": {"filename": "/tmp/backing.qcow2"}}} >> >> Who can tell me what has happened here? Oh, yes, the command failed, I >> would have guessed that from the "error" key. But the actual error >> description is as useless as it gets. It doesn't tell me anything about >> _why_ the snapshot couldn't be created. ("Permission denied" would have >> been the helpful additional information in this case) > > There's a function called qemu_fopen_err() in the screendump conversion series > that return more specific errors. It will be trivial to add qemu_open_err() > as soon as qemu_fopen_err() is merged. > > We're adding a bunch of more precise errors (some map directly to errno). That's > the easy part. The hard part is to convert everything to use them. > > Note that while it's true that this shouldn't have leaked to QMP, good error > reporting is a general problem in QEMU. I guess my point is that we're actually moving backwards here. In HMP things like this do print the right error message (using error_report). And the return code is passed all the way down to where the QMP error is generated, it's just ignored there. The last time I checked there was no easy way to handle it there because errno and strerror(-errno) aren't things allowed in QMP messages. This is the problem for which I wanted to get some attention. Does the patch that you mentioned add a generic way for adding an (converted) errno to QMP errors? Or does it split up existing errors into more and finer grained errors? Kevin