Re: [Xen-devel] [PATCH] xl: Return an error if an empty file is passed to cd-insert

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-05-13 at 10:35 +0100, Roger Pau Monne wrote:
> On 10/05/13 17:43, George Dunlap wrote:
> > Two changes:
> > * Stat the file before calling libxl_cdrom_insert()
> > * Return an error if anything fails (including libxl_cdrom_insert)
> > 
> > This is in part to work around the fact that the RAW disk type
> > is used for things that aren't actually files; so we can't call
> > stat in libxl_device.c:libxl__device_disk_set_backend() because
> > it may be going over a remote protocol.
> > 
> > Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> > CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
> > ---
> >  tools/libxl/xl_cmdimpl.c |   26 +++++++++++++++++++++-----
> >  1 file changed, 21 insertions(+), 5 deletions(-)
> > 
> > diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> > index c1a969b..e8ce35b 100644
> > --- a/tools/libxl/xl_cmdimpl.c
> > +++ b/tools/libxl/xl_cmdimpl.c
> > @@ -2505,25 +2505,42 @@ int main_memset(int argc, char **argv)
> >      return 0;
> >  }
> >  
> > -static void cd_insert(uint32_t domid, const char *virtdev, char *phys)
> > +static int cd_insert(uint32_t domid, const char *virtdev, char *phys)
> >  {
> >      libxl_device_disk disk; /* we don't free disk's contents */
> >      char *buf = NULL;
> >      XLU_Config *config = 0;
> > +    struct stat b;
> > +    int rc = 0;
> >  
> >  
> >      if (asprintf(&buf, "vdev=%s,access=r,devtype=cdrom,target=%s",
> >                   virtdev, phys ? phys : "") < 0) {
> >          fprintf(stderr, "out of memory\n");
> > -        return;
> > +        return 1;
> 
> ERROR_NOMEM

xl seems pretty inconsistent in its use of libxl error codes, sometimes
it uses +ERROR_FOO, other times -ERROR_FOO and other times it uses its
own open coded numbers.

So I wouldn't say this is wrong as such but so long as the final xl exit
code is 0 on success and non-zero otherwise I think it is up to George.
> 
> >      }
> >  
> >      parse_disk_config(&config, buf, &disk);
> >  
> > -    libxl_cdrom_insert(ctx, domid, &disk, NULL);
> > +    /* ATM the existence of the backing file is not checked for qdisk
> > +     * in libxl_cdrom_insert() because RAW is used for remote
> > +     * protocols as well as plain files.  This will ideally be changed
> > +     * for 4.4, but this work-around fixes the problem of "cd-insert"
> > +     * returning success for non-existent files. */
> > +    if (disk.format != LIBXL_DISK_FORMAT_EMPTY
> > +        && stat(disk.pdev_path, &b)) {
> > +        fprintf(stderr, "Cannot stat file: %s\n",
> > +                disk.pdev_path);
> 
> You are leaking buf here, I know xl is just about to exit,

I prefer to have xl clear up properly whenever possible. Not because I
care particularly about xl (which isn't generally long lived) but
because it makes it possible to use valgrind+xl to check for leaks in
libxl, and I care about that because other toolstacks which use libxl
can be long lived and therefore care about leaks. Having xl not contain
false positive leaks helps here.

Ian.


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