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From 9452583824b50cb6f095c5ec1894b38df7b01175 Mon Sep 17 00:00:00 2001
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Message-Id: <9452583824b50cb6f095c5ec1894b38df7b01175.1464449390.git.jen@redhat.com>
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In-Reply-To: <c7936395ecf322b3de37662c7c6b772e36866cc7.1464449390.git.jen@redhat.com>
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References: <c7936395ecf322b3de37662c7c6b772e36866cc7.1464449390.git.jen@redhat.com>
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Mon, 23 May 2016 11:28:41 -0400
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Subject: [CHANGE 3/3] block/raw-posix: Open file descriptor O_RDWR to work
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around glibc posix_fallocate emulation issue.
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To: rhvirt-patches@redhat.com,
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jen@redhat.com
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <1464002921-1079-2-git-send-email-kwolf@redhat.com>
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Patchwork-id: 70425
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O-Subject: [RHEL-7.3 qemu-kvm PATCH 1/1] block/raw-posix: Open file descriptor O_RDWR to work around glibc posix_fallocate emulation issue.
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Bugzilla: 1268345
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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RH-Acked-by: Richard Jones <rjones@redhat.com>
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From: "Richard W.M. Jones" <rjones@redhat.com>
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The following command fails on an NFS mountpoint:
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$ qemu-img create -f qcow2 -o preallocation=falloc disk.img 262144
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Formatting 'disk.img', fmt=qcow2 size=262144 encryption=off cluster_size=65536 preallocation='falloc' lazy_refcounts=off
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qemu-img: disk.img: Could not preallocate data for the new file: Bad file descriptor
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The reason turns out to be because NFS doesn't support the
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posix_fallocate call. glibc emulates it instead. However glibc's
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emulation involves using the pread(2) syscall. The pread syscall
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fails with EBADF if the file descriptor is opened without the read
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open-flag (ie. open (..., O_WRONLY)).
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I contacted glibc upstream about this, and their response is here:
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https://bugzilla.redhat.com/show_bug.cgi?id=1265196#c9
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There are two possible fixes: Use Linux fallocate directly, or (this
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fix) work around the problem in qemu by opening the file with O_RDWR
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instead of O_WRONLY.
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Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
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Reviewed-by: Jeff Cody <jcody@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 73ba05d936e82fe01b2b2cf987bf3aecb4792af5)
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Signed-off-by: Jeff E. Nelson <jen@redhat.com>
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---
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block/raw-posix.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/block/raw-posix.c b/block/raw-posix.c
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index 1f5275f..92fcb6c 100644
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--- a/block/raw-posix.c
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+++ b/block/raw-posix.c
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@@ -1265,7 +1265,7 @@ static int raw_create(const char *filename, QEMUOptionParameter *options,
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options++;
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}
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- fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
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+ fd = qemu_open(filename, O_RDWR | O_CREAT | O_TRUNC | O_BINARY,
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0644);
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if (fd < 0) {
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result = -errno;
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--
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2.5.5
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