On 03.06.21 15:37, Paolo Bonzini wrote:
Even though it was only called for devices that have bs->sg set (which
must be character devices),
sg_get_max_segments looked at /sys/dev/block which only works for
block devices.

On Linux the sg driver has its own way to provide the maximum number of
iovecs in a scatter/gather list.

Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
  block/file-posix.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/block/file-posix.c b/block/file-posix.c
index f37dfc10b3..58db526cc2 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1180,6 +1180,17 @@ static int sg_get_max_segments(int fd)
          goto out;
      }
+ if (S_ISCHR(st->st_mode)) {
+        if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
+            return ret;
+        }
+        return -EIO;
+    }
+
+    if (!S_ISBLK(st->st_mode)) {
+        return -ENOTSUP;
+    }
+

With %s/->/./:

Reviewed-by: Max Reitz <mre...@redhat.com>

(To answer Vladimir’s question, I don’t believe the condition should be bs->sg, because bs->sg == true is a given for this function anyway. Therefore, there’s no need to check whether the char device is an SG device.)


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