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.
Regards
Oliver
>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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