| Message ID | 1443542050-26720-1-git-send-email-rjones@redhat.com |
|---|---|
| State | New |
| Headers | show |
Am 29.09.2015 um 17:54 hat Richard W.M. Jones geschrieben: > 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 Thanks, applied to the block branch. Kevin
On Tue, Sep 29, 2015 at 04:54:10PM +0100, Richard W.M. Jones wrote: > 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 > --- > block/raw-posix.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > index 30df8ad..86f8562 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; > -- > 2.5.0 > > Reviewed-by: Jeff Cody <jcody@redhat.com>
On 09/29/2015 09:54 AM, Richard W.M. Jones wrote: > 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)). > Failing with EBADF feels fishy (POSIX requests EINVAL in that case) - but that's an upstream glibc discussion that has forked from this thread and doesn't hold up the qemu fix. > 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 > --- > block/raw-posix.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Reviewed-by: Eric Blake <eblake@redhat.com>
On 29 September 2015 at 16:54, Richard W.M. Jones <rjones@redhat.com> wrote: > 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 "You are not authorized to access bug #1265196." Any chance of a working URL if we're going to immortalize it in QEMU's git log? thanks -- PMM
On Fri, Oct 02, 2015 at 03:36:04PM +0100, Peter Maydell wrote: > On 29 September 2015 at 16:54, Richard W.M. Jones <rjones@redhat.com> wrote: > > 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 > > "You are not authorized to access bug #1265196." > > Any chance of a working URL if we're going to immortalize it > in QEMU's git log? Sorry about that. I have now made the bug public -- there was absolutely no reason why it was private before. Rich.
diff --git a/block/raw-posix.c b/block/raw-posix.c index 30df8ad..86f8562 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;
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 --- block/raw-posix.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)