[PATCH v2 1/5] file-posix: split hdev_refresh_limits from raw_refresh_limits

[Maxim Levitsky]

From: Tom Yan <tom.t...@gmail.com>

We can and should get max transfer length and max segments for all host
devices / cdroms (on Linux).

Also use MIN_NON_ZERO instead when we clamp max transfer length against
max segments.

Signed-off-by: Tom Yan <tom.t...@gmail.com>
Signed-off-by: Maxim Levitsky <mlevi...@redhat.com>
---
 block/file-posix.c | 59 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 43 insertions(+), 16 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index d5fd1dbcd2..226ddbbdad 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1162,6 +1162,12 @@ static void raw_reopen_abort(BDRVReopenState *state)
 
 static int sg_get_max_transfer_length(int fd)
 {
+    /*
+     * BLKSECTGET for /dev/sg* character devices incorrectly returns
+     * the max transfer size in bytes (rather than in blocks).
+     * Also note that /dev/sg* doesn't support BLKSSZGET ioctl.
+     */
+
 #ifdef BLKSECTGET
     int max_bytes = 0;
 
@@ -1175,7 +1181,22 @@ static int sg_get_max_transfer_length(int fd)
 #endif
 }
 
-static int sg_get_max_segments(int fd)
+static int get_max_transfer_length(int fd)
+{
+#if defined(BLKSECTGET)
+    int sect = 0;
+
+    if (ioctl(fd, BLKSECTGET, &sect) == 0) {
+        return sect << 9;
+    } else {
+        return -errno;
+    }
+#else
+    return -ENOSYS;
+#endif
+}
+
+static int get_max_segments(int fd)
 {
 #ifdef CONFIG_LINUX
     char buf[32];
@@ -1230,23 +1251,29 @@ static void raw_refresh_limits(BlockDriverState *bs, 
Error **errp)
 {
     BDRVRawState *s = bs->opaque;
 
-    if (bs->sg) {
-        int ret = sg_get_max_transfer_length(s->fd);
+    raw_probe_alignment(bs, s->fd, errp);
+    bs->bl.min_mem_alignment = s->buf_align;
+    bs->bl.opt_mem_alignment = MAX(s->buf_align, qemu_real_host_page_size);
+}
 
-        if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
-            bs->bl.max_transfer = pow2floor(ret);
-        }
+static void hdev_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+    BDRVRawState *s = bs->opaque;
 
-        ret = sg_get_max_segments(s->fd);
-        if (ret > 0) {
-            bs->bl.max_transfer = MIN(bs->bl.max_transfer,
-                                      ret * qemu_real_host_page_size);
-        }
+    int ret = bs->sg ? sg_get_max_transfer_length(s->fd) :
+                       get_max_transfer_length(s->fd);
+
+    if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
+        bs->bl.max_transfer = pow2floor(ret);
     }
 
-    raw_probe_alignment(bs, s->fd, errp);
-    bs->bl.min_mem_alignment = s->buf_align;
-    bs->bl.opt_mem_alignment = MAX(s->buf_align, qemu_real_host_page_size);
+    ret = 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);
+    }
+
+    raw_refresh_limits(bs, errp);
 }
 
 static int check_for_dasd(int fd)
@@ -3601,7 +3628,7 @@ static BlockDriver bdrv_host_device = {
     .bdrv_co_pdiscard       = hdev_co_pdiscard,
     .bdrv_co_copy_range_from = raw_co_copy_range_from,
     .bdrv_co_copy_range_to  = raw_co_copy_range_to,
-    .bdrv_refresh_limits = raw_refresh_limits,
+    .bdrv_refresh_limits = hdev_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
     .bdrv_io_unplug = raw_aio_unplug,
     .bdrv_attach_aio_context = raw_aio_attach_aio_context,
@@ -3725,7 +3752,7 @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_co_preadv         = raw_co_preadv,
     .bdrv_co_pwritev        = raw_co_pwritev,
     .bdrv_co_flush_to_disk  = raw_co_flush_to_disk,
-    .bdrv_refresh_limits = raw_refresh_limits,
+    .bdrv_refresh_limits = hdev_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
     .bdrv_io_unplug = raw_aio_unplug,
     .bdrv_attach_aio_context = raw_aio_attach_aio_context,
-- 
2.26.2