Re: [Qemu-devel] [PATCH] Fix qemu-img can't create qcow image based on read-only image

[Sheng Yang]

On Thursday 28 January 2010 17:17:22 Kevin Wolf wrote:
> Am 28.01.2010 06:22, schrieb Sheng Yang:
> > Commit 03cbdac7 "Disable fall-back to read-only when cannot open drive's
> > file for read-write" result in read-only image can't be used as backed
> > image in qemu-img.
> >
> > CC: Naphtali Sprei <address@hidden>
> > Signed-off-by: Sheng Yang <address@hidden>
> > ---
> >
> > This issue blocked our QA's KVM nightly test. But in fact, I don't like
> > this patch, feeling uncomfortable to change long existed interface... Any
> > alternative? Add a readonly command line would change the default
> > behavior(I don't think fall back to readonly looks like a bug); or even
> > revert the commit? What's the story behind it?
> >
> >  qemu-img.c |   15 ++++++++++-----
> >  1 files changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/qemu-img.c b/qemu-img.c
> > index 3cea8ce..f8be5cb 100644
> > --- a/qemu-img.c
> > +++ b/qemu-img.c
> > @@ -188,11 +188,13 @@ static int read_password(char *buf, int buf_size)
> >  #endif
> >
> >  static BlockDriverState *bdrv_new_open(const char *filename,
> > -                                       const char *fmt)
> > +                                       const char *fmt,
> > +                                       int readonly)
> >  {
> >      BlockDriverState *bs;
> >      BlockDriver *drv;
> >      char password[256];
> > +    int flags = BRDV_O_FLAGS;
> >
> >      bs = bdrv_new("");
> >      if (!bs)
> > @@ -204,7 +206,10 @@ static BlockDriverState *bdrv_new_open(const char
> > *filename, } else {
> >          drv = NULL;
> >      }
> > -    if (bdrv_open2(bs, filename, BRDV_O_FLAGS | BDRV_O_RDWR, drv) < 0) {
> > +    if (!readonly) {
> > +        flags |= BDRV_O_RDWR;
> > +    }
> > +    if (bdrv_open2(bs, filename, flags, drv) < 0) {
> >          error("Could not open '%s'", filename);
> >      }
> >      if (bdrv_is_encrypted(bs)) {
> > @@ -343,7 +348,7 @@ static int img_create(int argc, char **argv)
> >                  }
> >              }
> >
> > -            bs = bdrv_new_open(backing_file->value.s, fmt);
> > +            bs = bdrv_new_open(backing_file->value.s, fmt, 1);
> >              bdrv_get_geometry(bs, &size);
> >              size *= 512;
> >              bdrv_delete(bs);
> > @@ -627,7 +632,7 @@ static int img_convert(int argc, char **argv)
> >
> >      total_sectors = 0;
> >      for (bs_i = 0; bs_i < bs_n; bs_i++) {
> > -        bs[bs_i] = bdrv_new_open(argv[optind + bs_i], fmt);
> > +        bs[bs_i] = bdrv_new_open(argv[optind + bs_i], fmt, 0);
> 
> Shouldn't it be read-only here, too?
 
Yes. 

Seems you guys are OK with this solution(and I think it's reasonable to remove 
the fall back). I would update the patch, hopefully it can be applied soon and 
picked up by Marcelo to resolve our block issue...

-- 
regards
Yang, Sheng