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SubjectRe: [RFC/PATCH] usb-storage: wait for device scanning before mounting root
(Adding Cc: Matthew Wilcox)

Pekka J Enberg wrote:
> Add a new kernel config option CONFIG_LATE_ROOT_MOUNT that makes the kernel
> wait until background scanning of USB mass storage devices is complete before
> attempting to mount the root filesystem.
>
> The config option is an alternative to the root_delay= kernel parameter
> solution people currently use to boot from USB mass storage devices.
[...]
> drivers/scsi/scsi_scan.c | 2 ++
> drivers/usb/storage/usb.c | 3 +++
> include/linux/init.h | 12 ++++++++++++
> init/Kconfig | 5 +++++
> init/do_mounts.c | 32 ++++++++++++++++++++++++++++++++
> 5 files changed, 54 insertions(+)
>
> Index: linux-2.6/drivers/usb/storage/usb.c
> ===================================================================
> --- linux-2.6.orig/drivers/usb/storage/usb.c
> +++ linux-2.6/drivers/usb/storage/usb.c
> @@ -928,6 +928,7 @@ static int usb_stor_scan_thread(void * _
> /* Should we unbind if no devices were detected? */
> }
>
> + complete_root_scan();
> complete_and_exit(&us->scanning_done, 0);
> }
>
> @@ -1007,12 +1008,14 @@ static int storage_probe(struct usb_inte
> goto BadDevice;
> }
>
> + begin_root_scan();
> /* Start up the thread for delayed SCSI-device scanning */
> th = kthread_create(usb_stor_scan_thread, us, "usb-stor-scan");
> if (IS_ERR(th)) {
> printk(KERN_WARNING USB_STORAGE
> "Unable to start the device-scanning thread\n");
> quiesce_and_remove_host(us);
> + complete_root_scan();
> result = PTR_ERR(th);
> goto BadDevice;
> }
[...]
> Index: linux-2.6/drivers/scsi/scsi_scan.c
> ===================================================================
> --- linux-2.6.orig/drivers/scsi/scsi_scan.c
> +++ linux-2.6/drivers/scsi/scsi_scan.c
> @@ -1802,6 +1802,7 @@ static int do_scan_async(void *_data)
> struct async_scan_data *data = _data;
> do_scsi_scan_host(data->shost);
> scsi_finish_async_scan(data);
> + complete_root_scan();
> return 0;
> }
>
> @@ -1823,6 +1824,7 @@ void scsi_scan_host(struct Scsi_Host *sh
> return;
> }
>
> + begin_root_scan();
> p = kthread_run(do_scan_async, data, "scsi_scan_%d", shost->host_no);
> if (unlikely(IS_ERR(p)))
> do_scan_async(data);

Looks like you want complete_root_scan() after IS_ERR(p). Are there any
other thread exit paths which don't call complete_root_scan() yet?

Besides, can't you use the generic async scan facility of the SCSI stack
for your purpose? If not, can it be extended to make it usable?
--
Stefan Richter
-=====-==--- -=-- ==--=
http://arcgraph.de/sr/


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