From 9c8493d3a6d2e4d879d1ef67ff1abebd532c87a0 Mon Sep 17 00:00:00 2001

From: Paolo Bonzini <pbonzini@redhat.com>

Date: Fri, 16 Jul 2021 16:51:34 -0400

Subject: [PATCH 18/43] file-posix: try BLKSECTGET on block devices too, do not

 round to power of 2

RH-Author: Miroslav Rezanina <mrezanin@redhat.com>

RH-Bugzilla: 1957194

bs->sg is only true for character devices, but block devices can also

be used with scsi-block and scsi-generic.  Unfortunately BLKSECTGET

returns bytes in an int for /dev/sgN devices, and sectors in a short

for block devices, so account for that in the code.

The maximum transfer also need not be a power of 2 (for example I have

seen disks with 1280 KiB maximum transfer) so there's no need to pass

the result through pow2floor.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

(cherry picked from commit 18473467d55a20d643b6c9b3a52de42f705b4d35)

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block/file-posix.c | 57 +++++++++++++++++++++++++++-------------------

 1 file changed, 33 insertions(+), 24 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c

index 44325a635d..7b4ebf65d5 100644

--- a/block/file-posix.c

+++ b/block/file-posix.c

@@ -1173,22 +1173,27 @@ static void raw_reopen_abort(BDRVReopenState *state)

     s->reopen_state = NULL;

 }

-static int sg_get_max_transfer_length(int fd)

+static int hdev_get_max_hw_transfer(int fd, struct stat *st)

 {

 #ifdef BLKSECTGET

-    int max_bytes = 0;

-

-    if (ioctl(fd, BLKSECTGET, &max_bytes) == 0) {

-        return max_bytes;

+    if (S_ISBLK(st->st_mode)) {

+        unsigned short max_sectors = 0;

+        if (ioctl(fd, BLKSECTGET, &max_sectors) == 0) {

+            return max_sectors * 512;

+        }

     } else {

-        return -errno;

+        int max_bytes = 0;

+        if (ioctl(fd, BLKSECTGET, &max_bytes) == 0) {

+            return max_bytes;

+        }

     }

+    return -errno;

 #else

     return -ENOSYS;

 #endif

 }

-static int sg_get_max_segments(int fd)

+static int hdev_get_max_segments(int fd, struct stat *st)

 {

 #ifdef CONFIG_LINUX

     char buf[32];

@@ -1197,26 +1202,20 @@ static int sg_get_max_segments(int fd)

     int ret;

     int sysfd = -1;

     long max_segments;

-    struct stat st;

-

-    if (fstat(fd, &st)) {

-        ret = -errno;

-        goto out;

-    }

-    if (S_ISCHR(st.st_mode)) {

+    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)) {

+    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));

+                                major(st->st_rdev), minor(st->st_rdev));

     sysfd = open(sysfspath, O_RDONLY);

     if (sysfd == -1) {

         ret = -errno;

@@ -1253,23 +1252,33 @@ out:

 static void raw_refresh_limits(BlockDriverState *bs, Error **errp)

 {

     BDRVRawState *s = bs->opaque;

+    struct stat st;

-    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);

+

+    /*

+     * Maximum transfers are best effort, so it is okay to ignore any

+     * errors.  That said, based on the man page errors in fstat would be

+     * very much unexpected; the only possible case seems to be ENOMEM.

+     */

+    if (fstat(s->fd, &st)) {

+        return;

+    }

+

+    if (bs->sg || S_ISBLK(st.st_mode)) {

+        int ret = hdev_get_max_hw_transfer(s->fd, &st);

         if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {

-            bs->bl.max_hw_transfer = pow2floor(ret);

+            bs->bl.max_hw_transfer = ret;

         }

-        ret = sg_get_max_segments(s->fd);

+        ret = hdev_get_max_segments(s->fd, &st);

         if (ret > 0) {

             bs->bl.max_iov = 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);

 }

 static int check_for_dasd(int fd)

-- 

2.27.0