From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40541) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WDNG8-0002Mh-24 for qemu-devel@nongnu.org; Tue, 11 Feb 2014 19:01:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WDNG2-0003fI-1X for qemu-devel@nongnu.org; Tue, 11 Feb 2014 19:00:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:17427) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WDNG1-0003fB-QS for qemu-devel@nongnu.org; Tue, 11 Feb 2014 19:00:53 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s1C00qsl018248 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 11 Feb 2014 19:00:52 -0500 From: Juan Quintela Date: Wed, 12 Feb 2014 01:00:49 +0100 Message-Id: <1392163249-6983-1-git-send-email-quintela@redhat.com> Subject: [Qemu-devel] [PATCH v2] qemu_file: use fwrite() correctly List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org fwrite() returns the number of items written. But when there is one error, it can return a short write. In the particular bug that I was tracking, I did a migration to a read-only filesystem. And it was able to finish the migration correctly. fwrite() never returned a negative error code, the 1st time it returns 0, after that it returns 4096. (migration writes chunks of about 14000 bytes). And it was able to "complete" the migration with success (yes, reading the file was a bit more difficult). On the 1st fwrite() for the read-only filesystem, it returns an errno of -EPIPE, that is exactly what has failed. To add insult to injury, if your amount of memory was big enough (12GB on my case), it overwrote some important structure, and from them, malloc failed. This check makes the problem go away. Signed-off-by: Juan Quintela --- v2: a.k.a Paolo was right On the first call to fwrite() it returns 0, and errno is setup to EPIPE, exactly what we wanted. Once here, improve the commit message. qemu-file.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/qemu-file.c b/qemu-file.c index 9473b67..e5ec798 100644 --- a/qemu-file.c +++ b/qemu-file.c @@ -100,7 +100,14 @@ static int stdio_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, int size) { QEMUFileStdio *s = opaque; - return fwrite(buf, 1, size, s->stdio_file); + int res; + + res = fwrite(buf, 1, size, s->stdio_file); + + if (res != size) { + return -errno; + } + return res; } static int stdio_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size) -- 1.8.5.3