[SCSI] sr.c: Fix getting wrong size

Here's the problem. Try to do this on 2.6.12:
- Kill udev and HAL
- Insert a CD-ROM into a SCSI or USB CD-ROM drive
- Run dd if=/dev/scd0
- cat /sys/block/sr0/size
- Eject the CD, insert a different one
- Run dd if=/dev/scd0
This is likely to do "access beyond the end of device", if you let it
- cat /sys/block/sr0/size
This shows the size of a previous CD, even though dd was supposed
to revalidate the device.
- Run dd if=/dev/scd0
The second run of dd works correctly!

The bug was introduced in 2.5.31, when Al fixes the recursive opens
in partitioning. Before, the code worked like this:
- Block layer called cdrom_open directly
- cdrom_open called sr_open
- sr_open called check_disk_change
- check_disk_change called sr_media_change
- sr_media_change did cd->needs_disk_change=1
- before returning sr_open tested cd->needs_disk_change
  and called get_sector_size.

In 2.6.12, the check_disk_change is called from cdrom_open only. Thus:
- Block layer calls sr_bd_open
- sr_bd_open calls cdrom_open
- cdrom_open calls sr_open
- sr_open tests cd->needs_disk_change, which wasn't set yet; returns
- cdrom_open calls check_disk_change
- check_disk_change calls sr_media_change
- sr_media_change does cd->needs_disk_change=1, but nobody cares

Acked by: Alexander Viro <aviro@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
This commit is contained in:
Pete Zaitcev
2005-07-05 18:18:08 -07:00
committed by James Bottomley
parent 8224bfa84d
commit 51490c89f9
2 changed files with 2 additions and 23 deletions

View File

@ -33,7 +33,6 @@ typedef struct scsi_cd {
struct scsi_device *device;
unsigned int vendor; /* vendor code, see sr_vendor.c */
unsigned long ms_offset; /* for reading multisession-CD's */
unsigned needs_sector_size:1; /* needs to get sector size */
unsigned use:1; /* is this device still supportable */
unsigned xa_flag:1; /* CD has XA sectors ? */
unsigned readcd_known:1; /* drive supports READ_CD (0xbe) */