scsi: core: Introduce {init,exit}_cmd_priv()

The current behavior of the SCSI core is to clear driver-private data
before preparing a request for submission to the SCSI LLD. Make it possible
for SCSI LLDs to disable clearing of driver-private data.

These hooks will be used by a later patch, namely "scsi: ufs: Let the SCSI
core allocate per-command UFS data".

Link: https://lore.kernel.org/r/20200123035637.21848-2-bvanassche@acm.org
Cc: Tomas Winkler <tomas.winkler@intel.com>
Cc: Stanley Chu <stanley.chu@mediatek.com>
Cc: Bean Huo <beanhuo@micron.com>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Can Guo <cang@codeaurora.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Johannes Thumshirn <jth@kernel.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 258a428..9f20119 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1097,7 +1097,7 @@ static void scsi_cleanup_rq(struct request *rq)
        }
 }
 
-/* Called after a request has been started. */
+/* Called before a request is prepared. See also scsi_mq_prep_fn(). */
 void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
 {
        void *buf = cmd->sense_buffer;
@@ -1105,7 +1105,7 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
        struct request *rq = blk_mq_rq_from_pdu(cmd);
        unsigned int flags = cmd->flags & SCMD_PRESERVED_FLAGS;
        unsigned long jiffies_at_alloc;
-       int retries;
+       int retries, to_clear;
        bool in_flight;
 
        if (!blk_rq_is_scsi(rq) && !(flags & SCMD_INITIALIZED)) {
@@ -1116,9 +1116,15 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
        jiffies_at_alloc = cmd->jiffies_at_alloc;
        retries = cmd->retries;
        in_flight = test_bit(SCMD_STATE_INFLIGHT, &cmd->state);
-       /* zero out the cmd, except for the embedded scsi_request */
-       memset((char *)cmd + sizeof(cmd->req), 0,
-               sizeof(*cmd) - sizeof(cmd->req) + dev->host->hostt->cmd_size);
+       /*
+        * Zero out the cmd, except for the embedded scsi_request. Only clear
+        * the driver-private command data if the LLD does not supply a
+        * function to initialize that data.
+        */
+       to_clear = sizeof(*cmd) - sizeof(cmd->req);
+       if (!dev->host->hostt->init_cmd_priv)
+               to_clear += dev->host->hostt->cmd_size;
+       memset((char *)cmd + sizeof(cmd->req), 0, to_clear);
 
        cmd->device = dev;
        cmd->sense_buffer = buf;
@@ -1711,6 +1717,7 @@ static int scsi_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
        const bool unchecked_isa_dma = shost->unchecked_isa_dma;
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
        struct scatterlist *sg;
+       int ret = 0;
 
        if (unchecked_isa_dma)
                cmd->flags |= SCMD_UNCHECKED_ISA_DMA;
@@ -1726,14 +1733,24 @@ static int scsi_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
                cmd->prot_sdb = (void *)sg + scsi_mq_inline_sgl_size(shost);
        }
 
-       return 0;
+       if (shost->hostt->init_cmd_priv) {
+               ret = shost->hostt->init_cmd_priv(shost, cmd);
+               if (ret < 0)
+                       scsi_free_sense_buffer(unchecked_isa_dma,
+                                              cmd->sense_buffer);
+       }
+
+       return ret;
 }
 
 static void scsi_mq_exit_request(struct blk_mq_tag_set *set, struct request *rq,
                                 unsigned int hctx_idx)
 {
+       struct Scsi_Host *shost = set->driver_data;
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
 
+       if (shost->hostt->exit_cmd_priv)
+               shost->hostt->exit_cmd_priv(shost, cmd);
        scsi_free_sense_buffer(cmd->flags & SCMD_UNCHECKED_ISA_DMA,
                               cmd->sense_buffer);
 }

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 74dc7d4..7464394 100644 (file)
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -62,6 +62,9 @@ struct scsi_host_template {
                            void __user *arg);
 #endif
 
+       int (*init_cmd_priv)(struct Scsi_Host *shost, struct scsi_cmnd *cmd);
+       int (*exit_cmd_priv)(struct Scsi_Host *shost, struct scsi_cmnd *cmd);
+
        /*
         * The queuecommand function is used to queue up a scsi
         * command block to the LLDD.  When the driver finished