On Wed, 2019-07-03 at 09:50 -0500, Eric Blake wrote:
> On 6/30/19 10:08 AM, Maxim Levitsky wrote:
> > Regular block devices (/dev/sda*, /dev/nvme*, etc) interface is not limited
>
> The regular block device interface is
>
> or
>
> Regular block devices interfaces are
>
> > by the underlying storage limits, but rather the kernel block layer
> > takes care to split the requests that are too large/fragmented.
> >
> > Doing so allows us to have less overhead in qemu.
> >
> > Signed-off-by: Maxim Levitsky <mlevi...@redhat.com>
> > ---
> > block/file-posix.c | 16 +++++++---------
> > 1 file changed, 7 insertions(+), 9 deletions(-)
> >
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index ab05b51a66..66dad34f8a 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1038,15 +1038,13 @@ static void raw_reopen_abort(BDRVReopenState *state)
> > s->reopen_state = NULL;
> > }
> >
> > -static int hdev_get_max_transfer_length(BlockDriverState *bs, int fd)
> > +static int sg_get_max_transfer_length(BlockDriverState *bs, int fd)
> > {
> > #ifdef BLKSECTGET
> > int max_bytes = 0;
> > - short max_sectors = 0;
> > - if (bs->sg && ioctl(fd, BLKSECTGET, &max_bytes) == 0) {
> > +
> > + if (ioctl(fd, BLKSECTGET, &max_bytes) == 0) {
> > return max_bytes;
> > - } else if (!bs->sg && ioctl(fd, BLKSECTGET, &max_sectors) == 0) {
> > - return max_sectors << BDRV_SECTOR_BITS;
> > } else {
> > return -errno;
> > }
> > @@ -1055,7 +1053,7 @@ static int
> > hdev_get_max_transfer_length(BlockDriverState *bs, int fd)
> > #endif
> > }
> >
> > -static int hdev_get_max_segments(const struct stat *st)
> > +static int sg_get_max_segments(const struct stat *st)
> > {
> > #ifdef CONFIG_LINUX
> > char buf[32];
> > @@ -1106,12 +1104,12 @@ static void raw_refresh_limits(BlockDriverState
> > *bs, Error **errp)
> > struct stat st;
> >
> > if (!fstat(s->fd, &st)) {
> > - if (S_ISBLK(st.st_mode) || S_ISCHR(st.st_mode)) {
> > - int ret = hdev_get_max_transfer_length(bs, s->fd);
>
> Is it worth delaying the fstat()...
>
> > + if (bs->sg) {
> > + int ret = sg_get_max_transfer_length(bs, s->fd);
> > if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
> > bs->bl.max_transfer = pow2floor(ret);
> > }
> > - ret = hdev_get_max_segments(&st);
> > + ret = sg_get_max_segments(&st);
>
> ...until inside the if (bs->sg) condition, to avoid wasted work for
> other scenarios?
>
> > if (ret > 0) {
> > bs->bl.max_transfer = MIN(bs->bl.max_transfer,
> > ret * getpagesize());
> >
>
> Reviewed-by: Eric Blake <ebl...@redhat.com>
>
Thank you very much for the review. I'll send a V2 soon.
Best regards,
Maxim Levitsky
