diff options
| author | Richard W.M. Jones <rjones@redhat.com> | 2015-09-29 16:54:10 +0100 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2015-10-02 13:48:29 +0200 |
| commit | 73ba05d936e82fe01b2b2cf987bf3aecb4792af5 (patch) | |
| tree | 8402b957686a90af0310701e08cbc4319da12749 | |
| parent | 99b7e7756780cec03fe5175db0f53b2fffa9426b (diff) | |
block/raw-posix: Open file descriptor O_RDWR to work around glibc posix_fallocate emulation issue.
https://bugzilla.redhat.com/show_bug.cgi?id=1265196
The following command fails on an NFS mountpoint:
$ qemu-img create -f qcow2 -o preallocation=falloc disk.img 262144
Formatting 'disk.img', fmt=qcow2 size=262144 encryption=off cluster_size=65536 preallocation='falloc' lazy_refcounts=off
qemu-img: disk.img: Could not preallocate data for the new file: Bad file descriptor
The reason turns out to be because NFS doesn't support the
posix_fallocate call. glibc emulates it instead. However glibc's
emulation involves using the pread(2) syscall. The pread syscall
fails with EBADF if the file descriptor is opened without the read
open-flag (ie. open (..., O_WRONLY)).
I contacted glibc upstream about this, and their response is here:
https://bugzilla.redhat.com/show_bug.cgi?id=1265196#c9
There are two possible fixes: Use Linux fallocate directly, or (this
fix) work around the problem in qemu by opening the file with O_RDWR
instead of O_WRONLY.
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1265196
Reviewed-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
| -rw-r--r-- | block/raw-posix.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/block/raw-posix.c b/block/raw-posix.c index 30df8adf7f..86f8562b5f 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -1648,7 +1648,7 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp) goto out; } - fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, + fd = qemu_open(filename, O_RDWR | O_CREAT | O_TRUNC | O_BINARY, 0644); if (fd < 0) { result = -errno; |