+static struct scsi_host_cmd_pool *scsi_get_host_cmd_pool(gfp_t gfp_mask)
+{
+ struct scsi_host_cmd_pool *retval = NULL, *pool;
+ /*
+ * Select a command slab for this host and create it if not
+ * yet existent.
+ */
+ mutex_lock(&host_cmd_pool_mutex);
+ pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
+ &scsi_cmd_pool;
+ if (!pool->users) {
+ pool->cmd_slab = kmem_cache_create(pool->cmd_name,
+ sizeof(struct scsi_cmnd), 0,
+ pool->slab_flags, NULL);
+ if (!pool->cmd_slab)
+ goto fail;
+
+ pool->sense_slab = kmem_cache_create(pool->sense_name,
+ SCSI_SENSE_BUFFERSIZE, 0,
+ pool->slab_flags, NULL);
+ if (!pool->sense_slab) {
+ kmem_cache_destroy(pool->cmd_slab);
+ goto fail;
+ }
+ }
+
+ pool->users++;
+ retval = pool;
+ fail:
+ mutex_unlock(&host_cmd_pool_mutex);
+ return retval;
+}
+
+static void scsi_put_host_cmd_pool(gfp_t gfp_mask)
+{
+ struct scsi_host_cmd_pool *pool;
+
+ mutex_lock(&host_cmd_pool_mutex);
+ pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
+ &scsi_cmd_pool;
+ /*
+ * This may happen if a driver has a mismatched get and put
+ * of the command pool; the driver should be implicated in
+ * the stack trace
+ */
+ BUG_ON(pool->users == 0);
+
+ if (!--pool->users) {
+ kmem_cache_destroy(pool->cmd_slab);
+ kmem_cache_destroy(pool->sense_slab);
+ }
+ mutex_unlock(&host_cmd_pool_mutex);
+}
+
+/**
+ * scsi_allocate_command - get a fully allocated SCSI command
+ * @gfp_mask: allocation mask
+ *
+ * This function is for use outside of the normal host based pools.
+ * It allocates the relevant command and takes an additional reference
+ * on the pool it used. This function *must* be paired with
+ * scsi_free_command which also has the identical mask, otherwise the
+ * free pool counts will eventually go wrong and you'll trigger a bug.
+ *
+ * This function should *only* be used by drivers that need a static
+ * command allocation at start of day for internal functions.
+ */
+struct scsi_cmnd *scsi_allocate_command(gfp_t gfp_mask)
+{
+ struct scsi_host_cmd_pool *pool = scsi_get_host_cmd_pool(gfp_mask);
+
+ if (!pool)
+ return NULL;
+
+ return scsi_pool_alloc_command(pool, gfp_mask);
+}
+EXPORT_SYMBOL(scsi_allocate_command);
+
+/**
+ * scsi_free_command - free a command allocated by scsi_allocate_command
+ * @gfp_mask: mask used in the original allocation
+ * @cmd: command to free
+ *
+ * Note: using the original allocation mask is vital because that's
+ * what determines which command pool we use to free the command. Any
+ * mismatch will cause the system to BUG eventually.
+ */
+void scsi_free_command(gfp_t gfp_mask, struct scsi_cmnd *cmd)
+{
+ struct scsi_host_cmd_pool *pool = scsi_get_host_cmd_pool(gfp_mask);
+
+ /*
+ * this could trigger if the mask to scsi_allocate_command
+ * doesn't match this mask. Otherwise we're guaranteed that this
+ * succeeds because scsi_allocate_command must have taken a reference
+ * on the pool
+ */
+ BUG_ON(!pool);
+
+ scsi_pool_free_command(pool, cmd);
+ /*
+ * scsi_put_host_cmd_pool is called twice; once to release the
+ * reference we took above, and once to release the reference
+ * originally taken by scsi_allocate_command
+ */
+ scsi_put_host_cmd_pool(gfp_mask);
+ scsi_put_host_cmd_pool(gfp_mask);
+}
+EXPORT_SYMBOL(scsi_free_command);
+