On Sat, Jan 14, 2012 at 11:48:25PM +0100, Oliver Neukum wrote:
> Am Freitag, 13. Januar 2012, 17:20:10 schrieb Alan Stern:
>
> > > 2. scsi_autopm_get_device(sdev) is called unconditionally on each open.
> > > But according to the comment on the top of sd_release(). scsi_autopm_put_device(sdev)
> > > would be called only for the last close. Doesn't that mean that concurrent
> > > open calls for a disk disable autosuspend permanently?
> >
> > There ought to be an analogous comment for sd_open() -- it gets called
> > only for the first open.
> >
> > This means something different from what you're probably thinking. If
> > two separate systems calls to open(2) are made (either in the same
> > process or in different processes), followed by two calls to close(2),
> > then sd_open and sd_release will each be invoked twice.
> >
> > However, if open(2) is called once followed by dup(2), and close(2) is
> > called twice (for both the original fd and the fd returned by dup),
> > then sd_open and sd_release will both be invoked only once. Even
> > though there are two file descriptors, there's only one open file
> > reference.
> >
> > BTW, there's one other thing you need to know -- an error in your
> > patch. SCSI doesn't use the same scheme as USB for indicating whether
> > a driver supports autosuspend. Instead it uses PCI's scheme:
> >
>
> Thanks, that clears up everything.
> Sarah, here's a correct patch for testing.
Thanks Oliver! I can't test this until Wednesday, when I'm back in the
office where my USB DVD drive is.
Sarah Sharp
> From 4ebcfed1056f0c9e974c4cf5e92e8cb77a627046 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oliver@xxxxxxxxxx>
> Date: Sat, 14 Jan 2012 23:45:55 +0100
> Subject: [PATCH] SCSI:implement PM for sr
>
> This implements basic power management for SCSI disks.
>
> Signed-off-by: Oliver Neukum <oneukum@xxxxxxx>
> ---
> drivers/scsi/sr.c | 31 +++++++++++++++++++++++++++++--
> 1 files changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
> index 5fc97d2..91b545b 100644
> --- a/drivers/scsi/sr.c
> +++ b/drivers/scsi/sr.c
> @@ -508,16 +508,29 @@ static int sr_prep_fn(struct request_queue *q, struct request *rq)
>
> static int sr_block_open(struct block_device *bdev, fmode_t mode)
> {
> + struct scsi_device *sdev;
> struct scsi_cd *cd;
> int ret = -ENXIO;
> + int err;
>
> mutex_lock(&sr_mutex);
> cd = scsi_cd_get(bdev->bd_disk);
> + sdev = cd->device;
> +
> + err = scsi_autopm_get_device(sdev);
> + if (err) {
> + ret = -EIO;
> + goto err_out;
> + }
> +
> if (cd) {
> ret = cdrom_open(&cd->cdi, bdev, mode);
> - if (ret)
> + if (ret) {
> scsi_cd_put(cd);
> + scsi_autopm_put_device(sdev);
> + }
> }
> +err_out:
> mutex_unlock(&sr_mutex);
> return ret;
> }
> @@ -525,9 +538,12 @@ static int sr_block_open(struct block_device *bdev, fmode_t mode)
> static int sr_block_release(struct gendisk *disk, fmode_t mode)
> {
> struct scsi_cd *cd = scsi_cd(disk);
> + struct scsi_device *sdev = cd->device;
> +
> mutex_lock(&sr_mutex);
> cdrom_release(&cd->cdi, mode);
> scsi_cd_put(cd);
> + scsi_autopm_put_device(sdev);
> mutex_unlock(&sr_mutex);
> return 0;
> }
> @@ -615,6 +631,11 @@ static int sr_open(struct cdrom_device_info *cdi, int purpose)
> struct scsi_device *sdev = cd->device;
> int retval;
>
> + retval = scsi_autopm_get_device(sdev);
> + if (retval) {
> + retval = -EIO;
> + goto pm_error_out;
> + }
> /*
> * If the device is in error recovery, wait until it is done.
> * If the device is offline, then disallow any access to it.
> @@ -626,16 +647,19 @@ static int sr_open(struct cdrom_device_info *cdi, int purpose)
> return 0;
>
> error_out:
> + scsi_autopm_put_device(sdev);
> +pm_error_out:
> return retval;
> }
>
> static void sr_release(struct cdrom_device_info *cdi)
> {
> struct scsi_cd *cd = cdi->handle;
> + struct scsi_device *sdev = cd->device;
>
> if (cd->device->sector_size > 2048)
> sr_set_blocklength(cd, 2048);
> -
> + scsi_autopm_put_device(sdev);
> }
>
> static int sr_probe(struct device *dev)
> @@ -715,6 +739,7 @@ static int sr_probe(struct device *dev)
> dev_set_drvdata(dev, cd);
> disk->flags |= GENHD_FL_REMOVABLE;
> add_disk(disk);
> + scsi_autopm_put_device(sdev);
>
> sdev_printk(KERN_DEBUG, sdev,
> "Attached scsi CD-ROM %s\n", cd->cdi.name);
> @@ -964,7 +989,9 @@ static void sr_kref_release(struct kref *kref)
> static int sr_remove(struct device *dev)
> {
> struct scsi_cd *cd = dev_get_drvdata(dev);
> + struct scsi_device *sdev = cd->device;
>
> + scsi_autopm_get_device(sdev);
> blk_queue_prep_rq(cd->device->request_queue, scsi_prep_fn);
> del_gendisk(cd->disk);
>
> --
> 1.7.1
>
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