Re: [PATCH RFC v2 02/18] scsi: core: Resurrect scsi_{get,free}_host_dev()

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On 14/06/2022 20:33, Bart Van Assche wrote:

Hi Bart,

On 6/9/22 03:29, John Garry wrote:
+/**
+ * scsi_get_host_dev - Create a scsi_device that points to the host adapter itself
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
What does this mean? That part of the function description is not
clear to me.


Agreed, this text is just as it was before (it was originally deleted) but I can fix it up to make sense.

+ * @shost: Host that needs a scsi_device
                               ^^^^^^^^^^^^^
This is not detailed enough. Consider changing "a scsi_device" into
"a scsi device for allocating reserved commands from".

+ *
+ * Lock status: None assumed.
+ *
+ * Returns:     The scsi_device or NULL
+ *
+ * Notes:
+ *    Attach a single scsi_device to the Scsi_Host - this should
+ *    be made to look like a "pseudo-device" that points to the
+ *    HA itself.
+ *
+ *    Note - this device is not accessible from any high-level
+ *    drivers (including generics), which is probably not
+ *    optimal.  We can add hooks later to attach.

The "which is probably not optimal. We can add hooks later to attach."
part probably should be moved to the patch description.

ok


+ */
+struct scsi_device *scsi_get_host_dev(struct Scsi_Host *shost)
+{
+    struct scsi_device *sdev = NULL;
+    struct scsi_target *starget;
+
+    mutex_lock(&shost->scan_mutex);
+    if (!scsi_host_scan_allowed(shost))
+        goto out;
+    starget = scsi_alloc_target(&shost->shost_gendev, 0, shost->this_id);
^^^^^^^^^^^^^^^^^^
Is it guaranteed that this channel / id combination will not be used for
any other SCSI device?

Does it matter if the parent device is different?


What if shost->this_id == -1?

+    if (!starget)
+        goto out;
+
+    sdev = scsi_alloc_sdev(starget, 0, NULL);
+    if (sdev)
+        sdev->borken = 0;
+    else
+        scsi_target_reap(starget);
+    put_device(&starget->dev);
+ out:
+    mutex_unlock(&shost->scan_mutex);
+    return sdev;
+}
+EXPORT_SYMBOL(scsi_get_host_dev);

Elsewhere in the SCSI core "get..dev" means increment the reference count of
a SCSI device. Maybe scsi_alloc_host_dev() is a better name?

I think that the intention is to only use this once for a shost, i.e. get or allocate that scsi_device once and use it for the lifetime of the shost. But I can rename if you think it's better.


+/*
+ * These two functions are used to allocate and free a pseudo device
+ * which will connect to the host adapter itself rather than any
+ * physical device.  You must deallocate when you are done with the
+ * thing.  This physical pseudo-device isn't real and won't be available
+ * from any high-level drivers.
+ */

Please keep function comments in .c files because that makes it more likely
that the comment and the implementation will remain in sync.


fine, I can relocate this.

Thanks,
John



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