[PULL 13/28] file-posix: fix max_iov for /dev/sg devices

Paolo Bonzini posted 28 patches 4 years, 7 months ago
Maintainers: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Fam Zheng <fam@euphon.net>, Paolo Bonzini <pbonzini@redhat.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>, Max Reitz <mreitz@redhat.com>, Eric Blake <eblake@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, Richard Henderson <richard.henderson@linaro.org>, Markus Armbruster <armbru@redhat.com>
[PULL 13/28] file-posix: fix max_iov for /dev/sg devices
Posted by Paolo Bonzini 4 years, 7 months ago
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, so add support for it.  The block device
path is kept because it will be reinstated in the next patches.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Max Reitz <mreitz@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 b3fbb9bd63..b8dc19ce1a 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1178,6 +1178,17 @@ 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 -ENOTSUP;
+    }
+
+    if (!S_ISBLK(st.st_mode)) {
+        return -ENOTSUP;
+    }
+
     sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
                                 major(st.st_rdev), minor(st.st_rdev));
     sysfd = open(sysfspath, O_RDONLY);
-- 
2.31.1