scsi: core: Support allocating a pseudo SCSI device

Allocate a pseudo SCSI device if 'nr_reserved_cmds' has been set. Pseudo
SCSI devices have the SCSI ID <max_id>:U64_MAX so they won't clash with
any devices the LLD might create. Pseudo SCSI devices are excluded from
scanning and will not show up in sysfs. Additionally, pseudo SCSI
devices are skipped by shost_for_each_device(). This prevents that the
SCSI error handler tries to submit a reset to a non-existent logical
unit.

Do not allocate a budget map for pseudo SCSI devices since the
cmd_per_lun limit does not apply to pseudo SCSI devices.

Do not perform queue depth ramp up / ramp down for pseudo SCSI devices.

Pseudo SCSI devices will be used to send internal commands to a storage
device.

[ bvanassche: edited patch description / renamed host_sdev into
  pseudo_sdev / unexported scsi_get_host_dev() / modified error path in
  scsi_get_pseudo_dev() / skip pseudo devices in __scsi_iterate_devices()
  and also when calling sdev_init(), sdev_configure() and sdev_destroy().
  See also
  https://lore.kernel.org/linux-scsi/20211125151048.103910-2-hare@suse.de/ ]

Reviewed-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20251031204029.2883185-5-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 8b7f5fafa9e08dde4777b3e085d8708feb83f51e..ad1476fb50356d312401c54adb94f96fcb64c430 100644 (file)
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -307,6 +307,14 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
        if (error)
                goto out_del_dev;
 
+       if (shost->nr_reserved_cmds) {
+               shost->pseudo_sdev = scsi_get_pseudo_sdev(shost);
+               if (!shost->pseudo_sdev) {
+                       error = -ENOMEM;
+                       goto out_del_dev;
+               }
+       }
+
        scsi_proc_host_add(shost);
        scsi_autopm_put_host(shost);
        return error;

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 589ae28b2c8b3fbf9c0ba1f731a7cd8672277b5c..76cdad063f7bcdc8fec53f247eedc667d697fcfb 100644 (file)
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -831,8 +831,11 @@ struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
        spin_lock_irqsave(shost->host_lock, flags);
        while (list->next != &shost->__devices) {
                next = list_entry(list->next, struct scsi_device, siblings);
-               /* skip devices that we can't get a reference to */
-               if (!scsi_device_get(next))
+               /*
+                * Skip pseudo devices and also devices we can't get a
+                * reference to.
+                */
+               if (!scsi_device_is_pseudo_dev(next) && !scsi_device_get(next))
                        break;
                next = NULL;
                list = list->next;

diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index 5b2b19f5e8ec8a3214a44e6558d03bc3e8c96a9a..d07ec15d6c00264120708bf3e54dc4b3cdccd79a 100644 (file)
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -135,6 +135,7 @@ extern int scsi_complete_async_scans(void);
 extern int scsi_scan_host_selected(struct Scsi_Host *, unsigned int,
                                   unsigned int, u64, enum scsi_scan_mode);
 extern void scsi_forget_host(struct Scsi_Host *);
+struct scsi_device *scsi_get_pseudo_sdev(struct Scsi_Host *);
 
 /* scsi_sysctl.c */
 #ifdef CONFIG_SYSCTL

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index de039efef290cc40e48b307cb1835e7f3eae2930..7acbfcfc2172eb5b36b239f24e26b3d33850d30c 100644 (file)
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -349,6 +349,9 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 
        scsi_sysfs_device_initialize(sdev);
 
+       if (scsi_device_is_pseudo_dev(sdev))
+               return sdev;
+
        depth = sdev->host->cmd_per_lun ?: 1;
 
        /*
@@ -1070,6 +1073,9 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
 
        sdev->sdev_bflags = *bflags;
 
+       if (scsi_device_is_pseudo_dev(sdev))
+               return SCSI_SCAN_LUN_PRESENT;
+
        /*
         * No need to freeze the queue as it isn't reachable to anyone else yet.
         */
@@ -1213,6 +1219,12 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
        if (!sdev)
                goto out;
 
+       if (scsi_device_is_pseudo_dev(sdev)) {
+               if (bflagsp)
+                       *bflagsp = BLIST_NOLUN;
+               return SCSI_SCAN_LUN_PRESENT;
+       }
+
        result = kmalloc(result_len, GFP_KERNEL);
        if (!result)
                goto out_free_sdev;
@@ -2084,12 +2096,65 @@ void scsi_forget_host(struct Scsi_Host *shost)
  restart:
        spin_lock_irqsave(shost->host_lock, flags);
        list_for_each_entry(sdev, &shost->__devices, siblings) {
-               if (sdev->sdev_state == SDEV_DEL)
+               if (scsi_device_is_pseudo_dev(sdev) ||
+                   sdev->sdev_state == SDEV_DEL)
                        continue;
                spin_unlock_irqrestore(shost->host_lock, flags);
                __scsi_remove_device(sdev);
                goto restart;
        }
        spin_unlock_irqrestore(shost->host_lock, flags);
+
+       /*
+        * Remove the pseudo device last since it may be needed during removal
+        * of other SCSI devices.
+        */
+       if (shost->pseudo_sdev)
+               __scsi_remove_device(shost->pseudo_sdev);
 }
 
+/**
+ * scsi_get_pseudo_sdev() - Attach a pseudo SCSI device to a SCSI host
+ * @shost: Host that needs a pseudo SCSI device
+ *
+ * Lock status: None assumed.
+ *
+ * Returns:     The scsi_device or NULL
+ *
+ * Notes:
+ *     Attach a single scsi_device to the Scsi_Host. The primary aim for this
+ *     device is to serve as a container from which SCSI commands can be
+ *     allocated. Each SCSI command will carry a command tag allocated by the
+ *     block layer. These SCSI commands can be used by the LLDD to send
+ *     internal or passthrough commands without having to manage tag allocation
+ *     inside the LLDD.
+ */
+struct scsi_device *scsi_get_pseudo_sdev(struct Scsi_Host *shost)
+{
+       struct scsi_device *sdev = NULL;
+       struct scsi_target *starget;
+
+       guard(mutex)(&shost->scan_mutex);
+
+       if (!scsi_host_scan_allowed(shost))
+               goto out;
+
+       starget = scsi_alloc_target(&shost->shost_gendev, 0, shost->max_id);
+       if (!starget)
+               goto out;
+
+       sdev = scsi_alloc_sdev(starget, U64_MAX, NULL);
+       if (!sdev) {
+               scsi_target_reap(starget);
+               goto put_target;
+       }
+
+       sdev->borken = 0;
+
+put_target:
+       /* See also the get_device(dev) call in scsi_alloc_target(). */
+       put_device(&starget->dev);
+
+out:
+       return sdev;
+}

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 15ba493d2138685d4d31a983ef5b687384ff2a80..c37992147847a72f6f889097989d3c7450e1389b 100644 (file)
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -1406,6 +1406,9 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev)
        int error;
        struct scsi_target *starget = sdev->sdev_target;
 
+       if (WARN_ON_ONCE(scsi_device_is_pseudo_dev(sdev)))
+               return -EINVAL;
+
        error = scsi_target_add(starget);
        if (error)
                return error;
@@ -1513,7 +1516,7 @@ void __scsi_remove_device(struct scsi_device *sdev)
        kref_put(&sdev->host->tagset_refcnt, scsi_mq_free_tags);
        cancel_work_sync(&sdev->requeue_work);
 
-       if (sdev->host->hostt->sdev_destroy)
+       if (!scsi_device_is_pseudo_dev(sdev) && sdev->host->hostt->sdev_destroy)
                sdev->host->hostt->sdev_destroy(sdev);
        transport_destroy_device(dev);
 

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 4c106342c4ae1c14ab4765251b7d763922afaba2..9186310887114b5a1c0eca1bd95d8245ce047296 100644 (file)
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -589,6 +589,22 @@ static inline unsigned int sdev_id(struct scsi_device *sdev)
 #define scmd_id(scmd) sdev_id((scmd)->device)
 #define scmd_channel(scmd) sdev_channel((scmd)->device)
 
+/**
+ * scsi_device_is_pseudo_dev() - Whether a device is a pseudo SCSI device.
+ * @sdev: SCSI device to examine
+ *
+ * A pseudo SCSI device can be used to allocate SCSI commands but does not show
+ * up in sysfs. Additionally, the logical unit information in *@sdev is made up.
+ *
+ * This function tests the LUN number instead of comparing @sdev with
+ * @sdev->host->pseudo_sdev because this function may be called before
+ * @sdev->host->pseudo_sdev has been initialized.
+ */
+static inline bool scsi_device_is_pseudo_dev(struct scsi_device *sdev)
+{
+       return sdev->lun == U64_MAX;
+}
+
 /*
  * checks for positions of the SCSI state machine
  */

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 7b8f144ccf7d82fd8a422e229b80af0e905c8032..4f945a20d19854f7193380c85265834b71b8a101 100644 (file)
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -721,6 +721,12 @@ struct Scsi_Host {
        /* ldm bits */
        struct device           shost_gendev, shost_dev;
 
+       /*
+        * A SCSI device structure used for sending internal commands to the
+        * HBA. There is no corresponding logical unit inside the SCSI device.
+        */
+       struct scsi_device *pseudo_sdev;
+
        /*
         * Points to the transport data (if any) which is allocated
         * separately