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 <pbonz...@redhat.com>
---
block/file-posix.c | 67 ++++++++++++++++++++++++++--------------------
1 file changed, 38 insertions(+), 29 deletions(-)
diff --git a/block/file-posix.c b/block/file-posix.c
index 88e58d2863..ea102483b0 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1147,22 +1147,27 @@ 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];
@@ -1171,26 +1176,20 @@ 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;
@@ -1227,23 +1226,33 @@ out:
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);
-
- if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
- bs->bl.max_hw_transfer = pow2floor(ret);
- }
-
- ret = sg_get_max_segments(s->fd);
- if (ret > 0) {
- bs->bl.max_iov = ret;
- }
- }
+ struct stat st;
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 = ret;
+ }
+
+ ret = hdev_get_max_segments(s->fd, &st);
+ if (ret > 0) {
+ bs->bl.max_iov = ret;
+ }
+ }
}
static int check_for_dasd(int fd)
--
2.31.1
