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Re: [Qemu-devel] [PATCH] Improve error reporting on file access

From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH] Improve error reporting on file access
Date: Tue, 27 Oct 2009 17:51:43 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Mark McLoughlin <address@hidden> writes:

> On Thu, 2009-10-01 at 09:42 -0500, Justin M. Forbes wrote:
>> Author: Justin M. Forbes <address@hidden>
>> Date:   Thu Oct 1 09:34:56 2009 -0500
>>     Improve error reporting on file access
>>     By making the error reporting include strerror(errno), it gives the user
>>     a bit more indication as to why qemu failed.  This is particularly
>>     important for people running qemu as a non root user.
>>     Signed-off-by: Justin M. Forbes <address@hidden>
> Certainly looks sensible to me
> Not having this is hurting us in Fedora 12 because we've started running
> qemu as an unprivileged user and people are having a hard time figuring
> out the various errors they're seeing caused by the change. This should
> help them.
> Only concern is that errno might not be getting propagated correctly by
> some of these functions, but we can fix that later if so.

Here's one:

diff --git a/vl.c b/vl.c
index 7bfd415..70fd2ca 100644
--- a/vl.c
+++ b/vl.c
@@ -2232,8 +2232,8 @@ DriveInfo *drive_init(QemuOpts *opts, void *opaque,

     if (bdrv_open2(dinfo->bdrv, file, bdrv_flags, drv) < 0) {
-        fprintf(stderr, "qemu: could not open disk image %s\n",
-                        file);
+        fprintf(stderr, "qemu: could not open disk image %s: %s\n",
+                        file, strerror(errno));
         return NULL;

bdrv_open2() returns the error code.  Usually, it also leaves it in
errno, but not always.  Try:

    $ >mt.img
    $ ~/work/qemu/bld/qemu-img create -f qcow2 -b mt.img mt.qcow2
    Formatting 'mt.qcow2', fmt=qcow2 size=0 backing_file='mt.img' 
encryption=off cluster_size=0 
    $ qemu [...] -drive file=mt.qcow2
    qemu: could not open disk image mt.qcow2: Success

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