Re: [Qemu-devel] [PATCH 1/2 v1] blkdrv: Add queue limits parameters for sg block drive

[Cong Meng]

On Tue 21 Aug 2012 04:48:17 PM CST, Paolo Bonzini wrote:
> Il 21/08/2012 10:23, Cong Meng ha scritto:
> > +static void sg_get_queue_limits(BlockDriverState *bs, const char *filename)
> > +{
> > +    DIR *ffs;
> > +    struct dirent *d;
> > +    char path[MAXPATHLEN];
> > +
> > +    snprintf(path, MAXPATHLEN,
> > +             "/sys/class/scsi_generic/sg%s/device/block/",
> > +             filename + strlen("/dev/sg"));
> > +
> > +    ffs = opendir(path);
> > +    if (!ffs) {
> > +        return;
> > +    }
> > +
> > +    for (;;) {
> > +        d = readdir(ffs);
> > +        if (!d) {
> > +            return;
> > +        }
> > +
> > +        if (strcmp(d->d_name, ".") == 0 || strcmp(d->d_name, "..") == 0) {
> > +            continue;
> > +        }
> > +
> > +        break;
> > +    }
> > +
> > +    closedir(ffs);
> > +
> > +    pstrcat(path, MAXPATHLEN, d->d_name);
> > +    pstrcat(path, MAXPATHLEN, "/queue/");
> > +
> > +    read_queue_limit(path, "max_sectors_kb", &bs->max_sectors);
> > +    read_queue_limit(path, "max_segments", &bs->max_segments);
> > +    read_queue_limit(path, "max_segment_size", &bs->max_segment_size);
> > +}
>
> Using /sys/dev/block or /sys/dev/char seems easier, and lets you
> retrieve the parameters for block devices too.
what do you mean with "block devices"?   Using "/dev/sda" instead of 
"/dev/sg0"?

> However, I'm worried of the consequences this has for migration.  You
> could have the same physical disk accessed with two different HBAs, with
> different limits.  So I don't know if this can really be solved at all.
I know little about qemu migration now.  The pending scsi commands will 
be saved and
transfered to remote machine when starting migration?

Cong.

> Paolo