On Tue, 2021-06-08 at 15:16 +0200, Paolo Bonzini wrote:
> 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 | 44 ++++++++++++++++++++++++--------------------
> 1 file changed, 24 insertions(+), 20 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index c9746d3eb6..1439293f63 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1149,22 +1149,27 @@ 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) {
Again I would use the bs->sg for that.
> + 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];
> @@ -1173,26 +1178,20 @@ 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;
> @@ -1229,15 +1228,20 @@ 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 = 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;
> }
Roughly speaking this looks correct, but I might have missed something as well.
This is roughly the same as patches from Tom Yan which I carried in my series
https://www.mail-archive.com/qemu-devel@nongnu.org/msg768258.html
https://www.mail-archive.com/qemu-devel@nongnu.org/msg768262.html
I like a bit more how he created separate functions for /dev/sg and for all
other block devices.
Please take a look.
Also not related to this patch, you are missing my fix I did to the VPD limit
emulation, please consider taking
it into the series:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg768260.html
Best regards,
Maxim Levitsky
