(sometimes just a list) for the devices they control. There wasn't any
uniformity across the different bus types.
-The current driver model provides a comon, uniform data model for describing
+The current driver model provides a common, uniform data model for describing
a bus and the devices that can appear under the bus. The unified bus
model includes a set of common attributes which all busses carry, and a set
of common callbacks, such as device discovery during bus probing, bus
Microsoft (namely ACPI) ensures that almost every device on almost any bus
on an x86-compatible system can work within this paradigm. Of course,
not every bus is able to support all such operations, although most
-buses support a most of those operations.
+buses support most of those operations.
Downstream Access
struct pci_dev {
...
- struct device dev;
+ struct device dev; /* Generic device interface */
+ ...
};
-Note first that it is statically allocated. This means only one allocation on
-device discovery. Note also that it is at the _end_ of struct pci_dev. This is
-to make people think about what they're doing when switching between the bus
-driver and the global driver; and to prevent against mindless casts between
-the two.
+Note first that the struct device dev within the struct pci_dev is
+statically allocated. This means only one allocation on device discovery.
+
+Note also that that struct device dev is not necessarily defined at the
+front of the pci_dev structure. This is to make people think about what
+they're doing when switching between the bus driver and the global driver,
+and to discourage meaningless and incorrect casts between the two.
The PCI bus layer freely accesses the fields of struct device. It knows about
the structure of struct pci_dev, and it should know the structure of struct
-device. Individual PCI device drivers that have been converted the the current
+device. Individual PCI device drivers that have been converted to the current
driver model generally do not and should not touch the fields of struct device,
-unless there is a strong compelling reason to do so.
+unless there is a compelling reason to do so.
-This abstraction is prevention of unnecessary pain during transitional phases.
-If the name of the field changes or is removed, then every downstream driver
-will break. On the other hand, if only the bus layer (and not the device
-layer) accesses struct device, it is only that layer that needs to change.
+The above abstraction prevents unnecessary pain during transitional phases.
+If it were not done this way, then when a field was renamed or removed, every
+downstream driver would break. On the other hand, if only the bus layer
+(and not the device layer) accesses the struct device, it is only the bus
+layer that needs to change.
User Interface
By virtue of having a complete hierarchical view of all the devices in the
system, exporting a complete hierarchical view to userspace becomes relatively
easy. This has been accomplished by implementing a special purpose virtual
-file system named sysfs. It is hence possible for the user to mount the
-whole sysfs filesystem anywhere in userspace.
+file system named sysfs.
+
+Almost all mainstream Linux distros mount this filesystem automatically; you
+can see some variation of the following in the output of the "mount" command:
+
+$ mount
+...
+none on /sys type sysfs (rw,noexec,nosuid,nodev)
+...
+$
+
+The auto-mounting of sysfs is typically accomplished by an entry similar to
+the following in the /etc/fstab file:
+
+none /sys sysfs defaults 0 0
-This can be done permanently by providing the following entry into the
-/etc/fstab (under the provision that the mount point does exist, of course):
+or something similar in the /lib/init/fstab file on Debian-based systems:
-none /sys sysfs defaults 0 0
+none /sys sysfs nodev,noexec,nosuid 0 0
-Or by hand on the command line:
+If sysfs is not automatically mounted, you can always do it manually with:
# mount -t sysfs sysfs /sys
git.openpandora.org / pandora-kernel.git / blobdiff