On Thu, Jan 9, 2014 at 5:59 AM, Kevin Wolf <kw...@redhat.com> wrote: > I think if there is no bs->backing_hd->file, we should get the filename > from bs->backing_hd->filename instead of leaving it empty. > > In fact, can we always do that or does bs->backing_hd normally lack the > filename? If so, perhaps that is what we need to fix, so we can always > directly use bs->backing_hd->filename here.
In the NBD example, bs->backing_hd->filename is "". I can take a stab at your proposed fix but I'm not very familiar with this code. In particular, I don't know what bs->backing_file is actually used for. The patch that introduced the pstrcpy mentions hmp's info block command, but the output looks fine AFAICT: % ./x86_64-softmmu/qemu-system-x86_64 -monitor stdio -nographic file-overlay.qcow2 QEMU 1.7.50 monitor - type 'help' for more information (qemu) info block ide0-hd0: file-overlay.qcow2 (qcow2) Backing file: base.file (chain depth: 1) ... I'll take a look and report back. On Thu, Jan 9, 2014 at 5:59 AM, Kevin Wolf <kw...@redhat.com> wrote: > [ CCing Max, who was recently active in this area, for another opinion ] > > Am 08.01.2014 um 20:43 hat Peter Feiner geschrieben: >> When a backing file is opened such that (1) a protocol is directly >> used as the block driver and (2) the block driver has bdrv_file_open, >> bdrv_open_backing_file segfaults. The problem arises because >> bdrv_open_common returns without setting bd->backing_hd->file. >> >> To effect (1), you seem to have to use the -F flag in qemu-img. There >> are several block drivers that satisfy (2), such as "file" and "nbd". >> Here are some concrete examples: >> >> #!/bin/bash >> >> echo Test file format >> ./qemu-img create -f file base.file 1m >> ./qemu-img create -f qcow2 -F file -o backing_file=base.file\ >> file-overlay.qcow2 >> ./qemu-img convert -O raw file-overlay.qcow2 file-convert.raw >> >> echo Test nbd format >> SOCK=$PWD/nbd.sock >> ./qemu-img create -f raw base.raw 1m >> ./qemu-nbd -t -k $SOCK base.raw & >> trap "kill $!" EXIT >> while ! test -e $SOCK; do sleep 1; done >> ./qemu-img create -f qcow2 -F nbd -o backing_file=nbd:unix:$SOCK\ >> nbd-overlay.qcow2 >> ./qemu-img convert -O raw nbd-overlay.qcow2 nbd-convert.raw >> >> Without this patch, the two qemu-img convert commands segfault. >> >> This is a regression that was introduced in v1.7 by >> dbecebddfa4932d1c83915bcb9b5ba5984eb91be. >> >> Signed-off-by: Peter Feiner <pe...@gridcentric.ca> >> --- >> block.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/block.c b/block.c >> index 64e7d22..a4a172d 100644 >> --- a/block.c >> +++ b/block.c >> @@ -1016,8 +1016,9 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict >> *options, Error **errp) >> error_free(local_err); >> return ret; >> } >> - pstrcpy(bs->backing_file, sizeof(bs->backing_file), >> - bs->backing_hd->file->filename); >> + if (bs->backing_hd->file) >> + pstrcpy(bs->backing_file, sizeof(bs->backing_file), >> + bs->backing_hd->file->filename); >> return 0; >> } > > I think if there is no bs->backing_hd->file, we should get the filename > from bs->backing_hd->filename instead of leaving it empty. > > In fact, can we always do that or does bs->backing_hd normally lack the > filename? If so, perhaps that is what we need to fix, so we can always > directly use bs->backing_hd->filename here. > > Kevin