[Qemu-block] [PATCH v2 3/3] block: get max_transfer limit for char (scsi-generic) devices

[Eric Farman]

Commit 6f607174 introduced a routine to get the maximum number
of bytes for a single I/O transfer for block devices, however
scsi generic devices are character devices, not block.  Add
a condition for this, such that scsi generic devices can view
the same data.

Some tweaking of data is required, because the block and sg
ioctls return values in different scales (sectors versus
bytes).  So adjust hdev_get_max_transfer_length such that it
always returns a value in bytes.

Signed-off-by: Eric Farman <far...@linux.vnet.ibm.com>
---
 block/file-posix.c    | 10 ++++++----
 include/block/block.h |  1 +
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 2115155..94068ca 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -657,9 +657,11 @@ static int hdev_get_max_transfer_length(BlockDriverState 
*bs, int fd)
     int max_sectors = 0;
     short max_sectors_short = 0;
     if (bs->sg && ioctl(fd, BLKSECTGET, &max_sectors) == 0) {
+        /* sg returns a value in bytes */
         return max_sectors;
     } else if (!bs->sg && ioctl(fd, BLKSECTGET, &max_sectors_short) == 0) {
-        return max_sectors_short;
+        /* block returns a value in sectors */
+        return max_sectors_short << BDRV_SECTOR_BITS;
     } else {
         return -errno;
     }
@@ -674,10 +676,10 @@ static void raw_refresh_limits(BlockDriverState *bs, 
Error **errp)
     struct stat st;
 
     if (!fstat(s->fd, &st)) {
-        if (S_ISBLK(st.st_mode)) {
+        if (S_ISBLK(st.st_mode) || S_ISCHR(st.st_mode)) {
             int ret = hdev_get_max_transfer_length(bs, s->fd);
-            if (ret > 0 && ret <= BDRV_REQUEST_MAX_SECTORS) {
-                bs->bl.max_transfer = pow2floor(ret << BDRV_SECTOR_BITS);
+            if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
+                bs->bl.max_transfer = pow2floor(ret);
             }
         }
     }
diff --git a/include/block/block.h b/include/block/block.h
index 8b0dcda..4e81f20 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -116,6 +116,7 @@ typedef struct HDGeometry {
 
 #define BDRV_REQUEST_MAX_SECTORS MIN(SIZE_MAX >> BDRV_SECTOR_BITS, \
                                      INT_MAX >> BDRV_SECTOR_BITS)
+#define BDRV_REQUEST_MAX_BYTES (BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS)
 
 /*
  * Allocation status flags
-- 
2.8.4