On Tue 21 Aug 2012 04:48:17 PM CST, Paolo Bonzini wrote:

Il 21/08/2012 10:23, Cong Meng ha scritto:

quoted

+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