From: Tom Yan <tom.ty89@gmail.com>
sg devices have different major/minor than their corresponding
block devices. Using sysfs to get max segments never really worked
for them.
Fortunately the sg driver provides an ioctl to get sg_tablesize,
which is apparently equivalent to max segments.
Signed-off-by: Tom Yan <tom.ty89@gmail.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
block/file-posix.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/block/file-posix.c b/block/file-posix.c
index cbf1271773..2bf4d095a7 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1179,6 +1179,26 @@ static int sg_get_max_transfer_length(int fd)
#endif
}
+static int sg_get_max_segments(int fd)
+{
+ /*
+ * /dev/sg* character devices report 'max_segments' via
+ * SG_GET_SG_TABLESIZE ioctl
+ */
+
+#ifdef SG_GET_SG_TABLESIZE
+ long max_segments = 0;
+
+ if (ioctl(fd, SG_GET_SG_TABLESIZE, &max_segments) == 0) {
+ return max_segments;
+ } else {
+ return -errno;
+ }
+#else
+ return -ENOSYS;
+#endif
+}
+
static int get_max_transfer_length(int fd)
{
#if defined(BLKSECTGET)
@@ -1265,7 +1285,7 @@ static void hdev_refresh_limits(BlockDriverState *bs,
Error **errp)
bs->bl.max_transfer = pow2floor(ret);
}
- ret = get_max_segments(s->fd);
+ ret = bs->sg ? sg_get_max_segments(s->fd) : get_max_segments(s->fd);
if (ret > 0) {
bs->bl.max_transfer = MIN_NON_ZERO(bs->bl.max_transfer,
ret * qemu_real_host_page_size);