[PATCH v2 02/11] qemu: Drop two layers of nesting of memoryBackingDir

[Daniel P. Berrangé]

On Mon, Mar 30, 2020 at 06:16:29PM +0200, Michal Prívozník wrote:
> On 30. 3. 2020 13:09, Daniel P. Berrangé wrote:
> > On Thu, Mar 26, 2020 at 04:15:06PM +0100, Michal Privoznik wrote:
> >> Initially introduced in v3.10.0-rc1~172.
> >>
> >> When generating a path for memory-backend-file or -mem-path, qemu
> >> driver will use the following pattern:
> >>
> >>   $memoryBackingDir/libvirt/qemu/$id-$shortName
> >>
> >> where $memoryBackingDir defaults to /var/lib/libvirt/qemu/ram but
> >> can be overridden in qemu.conf. Anyway, the "/libvirt/qemu/" part
> >> looks redundant, because it's already contained in the default,
> >> or creates unnecessary nesting if overridden in qemu.conf.
> > 
> > I think this was copied from our earlier huge pages code
> > which used /dev/hugepages, and then added "/libvirt/qemu"
> > to it.
> > 
> > Now we're stripping off "/libvirt/qemu" though, we're liable
> > to a filename clashes if someone edits qemu.conf to point to
> > /dev/shm.
> > 
> > IOW, even though "/libvirt/qemu" is redundant when using our
> > default path, I think we need to keep it to avoid clashing
> > with custom paths.
> 
> Alright. So what if I'd squash this in?
> 
> diff --git i/src/qemu/qemu_conf.c w/src/qemu/qemu_conf.c
> index 9786e19f8f..2ead5d5920 100644
> --- i/src/qemu/qemu_conf.c
> +++ w/src/qemu/qemu_conf.c
> @@ -970,7 +970,18 @@ static int
>  virQEMUDriverConfigLoadMemoryEntry(virQEMUDriverConfigPtr cfg,
>                                     virConfPtr conf)
>  {
> -    return virConfGetValueString(conf, "memory_backing_dir", &cfg->memoryBackingDir);
> +    char *dir = NULL;
> +    int rc;
> +
> +    if ((rc = virConfGetValueString(conf, "memory_backing_dir", &dir)) < 0) {
> +        return -1;
> +    } else if (rc > 0) {
> +        VIR_FREE(cfg->memoryBackingDir);
> +        cfg->memoryBackingDir = g_strdup_printf("%s/libvirt/qemu", dir);
> +        return 1;
> +    }
> +
> +    return 0;
>  }
> 
> 
> This way we would drop "/libvirt/qemu" in the default configuration and keep it if user overrides it in qemu.conf.

Yeah, I think that works.

Regards,
Daniel
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