| Message ID | 20201217165612.942849-1-mlevitsk@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | SCSI: fix transfer limits for SCSI passthrough | expand |
On Thu, 2020-12-17 at 18:56 +0200, Maxim Levitsky wrote: > This patch series attempts to provide a solution to the problem of the transfer > limits of the raw file driver (host_device/file-posix), some of which I > already tried to fix in the past. > > I included 2 patches from Tom Yan which fix two issues with reading the limits > correctly from the */dev/sg* character devices in the first place. > > The only change to these patches is that I tweaked a bit the comments in the > source to better document the /dev/sg quirks. > > The other two patches in this series split the max transfer limits that qemu > block devices expose in two: > One limit is for the regular IO, and another is for the SG_IO (aka bdrv_*_ioctl), > and the two device drivers (scsi-block and scsi-generic) that use the later > are switched to the new interface. > > This should ensure that the raw driver can still advertise the unlimited > transfer length, unless it is used for SG_IO, because that yields the highest > performance. > > Also I include a somewhat unrelated fix to a bug I found in qemu's > SCSI passthrough while testing this: > When qemu emulates the VPD block limit page, for a SCSI device that doesn't > implement it, it doesn't really advertise the emulated page to the guest. > > I tested this by doing both regular and SG_IO passthrough of my > USB SD card reader. > > That device turned out to be a perfect device for the task, since it has max > transfer size of 1024 blocks (512K), and it enforces it. > > Also it didn't implement the VPD block limits page, > (transfer size limit probably comes from something USB related) which triggered > the unrelated bug. > > I was able to see IO errors without the patches, and the wrong max transfer > size in the guest, and with patches both issues were gone. > > I also found an unrelated issue in /dev/sg passthrough in the kernel. > It turns out that in-kernel driver has a limitation of 16 requests in flight, > regardless of what underlying device supports. > > With a large multi-threaded fio job and a debug print in qemu, it is easy to > see it, although the errors don't do much harm to the guest as it retries the > IO, and eventually succeed. > It is an open question if this should be solved. > > V2: fixed an issue in a patch from Tom Yan (thanks), and removed > refactoring from last patch according to Paulo's request. > > V3: few cosmitic changes due to the review feedback. > > Maxim Levitsky (3): > block: add max_ioctl_transfer to BlockLimits > block: use blk_get_max_ioctl_transfer for SCSI passthrough > block/scsi: correctly emulate the VPD block limits page > > Tom Yan (2): > file-posix: split hdev_refresh_limits from raw_refresh_limits > file-posix: add sg_get_max_segments that actually works with sg > > block/block-backend.c | 12 ++++++ > block/file-posix.c | 76 +++++++++++++++++++++++++++------- > block/io.c | 2 + > block/iscsi.c | 1 + > hw/scsi/scsi-generic.c | 13 ++++-- > include/block/block_int.h | 4 ++ > include/sysemu/block-backend.h | 1 + > 7 files changed, 90 insertions(+), 19 deletions(-) > > -- > 2.26.2 > > > Any update on this? Best regards, Maxim Levitsky