diff mbox series

[2/5] file-posix: add sg_get_max_segments that actually works with sg

Message ID 20201104173217.417538-3-mlevitsk@redhat.com
State New
Headers show
Series [1/5] file-posix: split hdev_refresh_limits from raw_refresh_limits | expand

Commit Message

Maxim Levitsky Nov. 4, 2020, 5:32 p.m. UTC 
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 mbox series

Patch

diff --git a/block/file-posix.c b/block/file-posix.c
index 6581f41b2b..c4df757504 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1181,6 +1181,26 @@  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) && defined(BLKSSZGET)
@@ -1269,7 +1289,7 @@  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);