Chapter 6: Device Drivers
blkdev_open
bd_acquire
do_open
get_gendisk
disk->fops->open
flag 0_EXCL set? bd_claim
Figure 6-13: Code flow diagram for
blkdev_open.
bd_acquirefirst finds the matchingblock_deviceinstance for the device. The pointer to the instance can
be read directly frominode->i_bdevif the device has already been used. Otherwise, it is created using
thedev_tinformation. Afterwarddo_opencarries out the main portion of the task, described below.
If exclusive access to the block device is requested by setting the flagO_EXCL, then the block device is
claimed withbd_claim. This sets thefileinstance associated with the device file as current holder of the
block device.
Main device?
Partition information invalid?
Insert block_device into data structures
Partition information invalid
Yes
No
Yes
No
do_open
get_gendisk
disk->fops->open
disk->fops->open
rescan_partitions
rescan_partitions
Device opened before?
Partition?
Figure 6-14: Code flow diagram fordo_open.
The first step ofdo_openis to callget_gendisk. This delivers thegendiskinstance that belongs to the
block device. Recall that thegendiskstructure describes the partitions of the block device as discussed in
Section 6.2.5. However, if the block device is opened for the first time, the information is not yet complete.
Nevertheless, the device-specificblock_device_operationsthat are required to work with the device
can already be found in the generic hard disk structure.
The kernel then needs to proceed differently depending on the type and state of the block device, as is
shown in Figure 6-14. Things are simpler if the block device has been opened before, as can be inferred
from the openers countblock_device->bd_openers.
