kernel/include/scsi/scsi_host.h, branch linux-3.17.y

scsi: add support for a blk-mq based I/O path.

2014-07-25T21:16:28Z

This patch adds support for an alternate I/O path in the scsi midlayer which uses the blk-mq infrastructure instead of the legacy request code. Use of blk-mq is fully transparent to drivers, although for now a host template field is provided to opt out of blk-mq usage in case any unforseen incompatibilities arise. In general replacing the legacy request code with blk-mq is a simple and mostly mechanical transformation. The biggest exception is the new code that deals with the fact the I/O submissions in blk-mq must happen from process context, which slightly complicates the I/O completion handler. The second biggest differences is that blk-mq is build around the concept of preallocated requests that also include driver specific data, which in SCSI context means the scsi_cmnd structure. This completely avoids dynamic memory allocations for the fast path through I/O submission. Due the preallocated requests the MQ code path exclusively uses the host-wide shared tag allocator instead of a per-LUN one. This only affects drivers actually using the block layer provided tag allocator instead of their own. Unlike the old path blk-mq always provides a tag, although drivers don't have to use it. For now the blk-mq path is disable by defauly and must be enabled using the "use_blk_mq" module parameter. Once the remaining work in the block layer to make blk-mq more suitable for slow devices is complete I hope to make it the default and eventually even remove the old code path. Based on the earlier scsi-mq prototype by Nicholas Bellinger. Thanks to Bart Van Assche and Robert Elliot for testing, benchmarking and various sugestions and code contributions. Signed-off-by: Christoph Hellwig Reviewed-by: Martin K. Petersen Reviewed-by: Hannes Reinecke Reviewed-by: Webb Scales Acked-by: Jens Axboe Tested-by: Bart Van Assche Tested-by: Robert Elliott

scsi: fix the {host,target,device}_blocked counter mess

2014-07-25T21:15:48Z

Seems like these counters are missing any sort of synchronization for updates, as a over 10 year old comment from me noted. Fix this by using atomic counters, and while we're at it also make sure they are in the same cacheline as the _busy counters and not needlessly stored to in every I/O completion. With the new model the _busy counters can temporarily go negative, so all the readers are updated to check for > 0 values. Longer term every successful I/O completion will reset the counters to zero, so the temporarily negative values will not cause any harm. Signed-off-by: Christoph Hellwig Reviewed-by: Martin K. Petersen Reviewed-by: Webb Scales Acked-by: Jens Axboe Tested-by: Bart Van Assche Tested-by: Robert Elliott

scsi: convert host_busy to atomic_t

2014-07-25T11:43:43Z

Avoid taking the host-wide host_lock to check the per-host queue limit. Instead we do an atomic_inc_return early on to grab our slot in the queue, and if necessary decrement it after finishing all checks. Signed-off-by: Christoph Hellwig Reviewed-by: Martin K. Petersen Reviewed-by: Hannes Reinecke Reviewed-by: Webb Scales Acked-by: Jens Axboe Tested-by: Bart Van Assche Tested-by: Robert Elliott

scsi: remove various exports that were only used by scsi_tgt

2014-07-17T20:07:45Z

Signed-off-by: Christoph Hellwig Reviewed-by: Paolo Bonzini Reviewed-by: Hannes Reinecke

tgt: removal

2014-07-17T20:07:44Z

Now that the ibmvstgt driver as the only user of scsi_tgt is gone, the scsi_tgt kernel module, the CONFIG_SCSI_TGT, CONFIG_SCSI_SRP_TGT_ATTRS and CONFIG_SCSI_FC_TGT_ATTRS kbuild variable, the scsi_host_template transfer_response method are no longer needed. [hch: minor updates to the current tree, changelog update] Signed-off-by: Bart Van Assche Signed-off-by: Christoph Hellwig Reviewed-by: Paolo Bonzini Reviewed-by: Hannes Reinecke

scsi: use 64-bit value for 'max_luns'

2014-07-17T20:07:38Z

Now that we're using 64-bit LUNs internally we need to increase the size of max_luns to 64 bits, too. Signed-off-by: Hannes Reinecke Reviewed-by: Christoph Hellwig Reviewed-by: Ewan Milne Signed-off-by: Christoph Hellwig

scsi: increase upper limit for max_sectors

2014-07-17T20:07:30Z

max_sectors in struct Scsi_Host specifies maximum number of sectors allowed in a single SCSI command. The data type of max_sectors is unsigned short, so the maximum transfer length per SCSI command is limited to less than 256MB in 4096-bytes sector size. (0xffff * 4096) This commit increases the SCSI mid level's limitation for max_sectors upto the block layer's limitation for max_hw_sectors by extending the data type of max_sectors in struct Scsi_Host and scsi_host_template, so that SCSI lower level drivers can specify more than 0xffff. Signed-off-by: Akinobu Mita Reviewed-by: Martin K. Petersen Signed-off-by: Christoph Hellwig

[SCSI] add support for per-host cmd pools

2014-03-27T15:26:33Z

This allows drivers to specify the size of their per-command private data in the host template and then get extra memory allocated for each command instead of needing another allocation in ->queuecommand. With the current SCSI code that already does multiple allocations for each command this probably doesn't make a big performance impact, but it allows to clean up the drivers, and prepare them for using the blk-mq infrastructure where the common allocation will make a difference. Signed-off-by: Christoph Hellwig Reviewed-by: Paolo Bonzini Signed-off-by: James Bottomley

[SCSI] improved eh timeout handler

2013-12-19T15:39:02Z

When a command runs into a timeout we need to send an 'ABORT TASK' TMF. This is typically done by the 'eh_abort_handler' LLDD callback. Conceptually, however, this function is a normal SCSI command, so there is no need to enter the error handler. This patch implements a new scsi_abort_command() function which invokes an asynchronous function scsi_eh_abort_handler() to abort the commands via the usual 'eh_abort_handler'. If abort succeeds the command is either retried or terminated, depending on the number of allowed retries. However, 'eh_eflags' records the abort, so if the retry would fail again the command is pushed onto the error handler without trying to abort it (again); it'll be cleared up from SCSI EH. [hare: smatch detected stray switch fixed] Signed-off-by: Hannes Reinecke Signed-off-by: James Bottomley

[SCSI] Disable WRITE SAME for RAID and virtual host adapter drivers

2013-11-29T04:48:39Z

Some host adapters do not pass commands through to the target disk directly. Instead they provide an emulated target which may or may not accurately report its capabilities. In some cases the physical device characteristics are reported even when the host adapter is processing commands on the device's behalf. This can lead to adapter firmware hangs or excessive I/O errors. This patch disables WRITE SAME for devices connected to host adapters that provide an emulated target. Driver writers can disable WRITE SAME by setting the no_write_same flag in the host adapter template. [jejb: fix up rejections due to eh_deadline patch] Signed-off-by: Martin K. Petersen Cc: stable@kernel.org Signed-off-by: James Bottomley