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 for /dev/sgN devices and sectors 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 | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-) diff --git a/block/file-posix.c b/block/file-posix.c index 9e316a2a97..e37a6bb8de 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1173,13 +1173,13 @@ static void raw_reopen_abort(BDRVReopenState *state) s->reopen_state = NULL; } -static int sg_get_max_transfer_length(int fd) +static int sg_get_max_transfer_length(int fd, struct stat *st) { #ifdef BLKSECTGET int max_bytes = 0; if (ioctl(fd, BLKSECTGET, &max_bytes) == 0) { - return max_bytes; + return S_ISBLK(st->st_mode) ? max_bytes * 512 : max_bytes; } else { return -errno; } @@ -1188,7 +1188,7 @@ static int sg_get_max_transfer_length(int fd) #endif } -static int sg_get_max_segments(int fd) +static int sg_get_max_segments(int fd, struct stat *st) { #ifdef CONFIG_LINUX char buf[32]; @@ -1197,15 +1197,9 @@ 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; - } 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; @@ -1242,15 +1236,20 @@ out: static void raw_refresh_limits(BlockDriverState *bs, Error **errp) { BDRVRawState *s = bs->opaque; + struct stat st; + + if (fstat(s->fd, &st)) { + return; + } - if (bs->sg) { - int ret = sg_get_max_transfer_length(s->fd); + if (bs->sg || S_ISBLK(st.st_mode)) { + int ret = sg_get_max_transfer_length(s->fd, &st); if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) { - bs->bl.max_transfer = pow2floor(ret); + bs->bl.max_transfer = ret; } - ret = sg_get_max_segments(s->fd); + ret = sg_get_max_segments(s->fd, &st); if (ret > 0) { bs->bl.max_iov = ret; } -- 2.30.1