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What: /dev/fw[0-9]+
Date: May 2007
KernelVersion: 2.6.22
The character device files /dev/fw* are the interface between
firewire-core and IEEE 1394 device drivers implemented in
userspace. The ioctl(2)- and read(2)-based ABI is defined and
documented in <linux/firewire-cdev.h>.
This ABI offers most of the features which firewire-core also
exposes to kernelspace IEEE 1394 drivers.
Each /dev/fw* is associated with one IEEE 1394 node, which can
be remote or local nodes. Operations on a /dev/fw* file have
different scope:
- The 1394 node which is associated with the file:
- Asynchronous request transmission
- Get the Configuration ROM
- Query node ID
- Query maximum speed of the path between this node
and local node
- The 1394 bus (i.e. "card") to which the node is attached to:
- Isochronous stream transmission and reception
- Asynchronous stream transmission and reception
- Asynchronous broadcast request transmission
- PHY packet transmission and reception
- Allocate, reallocate, deallocate isochronous
resources (channels, bandwidth) at the bus's IRM
- Query node IDs of local node, root node, IRM, bus
- Query cycle time
- Bus reset initiation, bus reset event reception
- All 1394 buses:
- Allocation of IEEE 1212 address ranges on the local
link layers, reception of inbound requests to such
an address range, asynchronous response transmission
to inbound requests
- Addition of descriptors or directories to the local
nodes' Configuration ROM
Due to the different scope of operations and in order to let
userland implement different access permission models, some
operations are restricted to /dev/fw* files that are associated
with a local node:
- Addition of descriptors or directories to the local
nodes' Configuration ROM
- PHY packet transmission and reception
A /dev/fw* file remains associated with one particular node
during its entire life time. Bus topology changes, and hence
node ID changes, are tracked by firewire-core. ABI users do not
need to be aware of topology.
The following file operations are supported:
Currently the only useful flags are O_RDWR.
Initiate various actions. Some take immediate effect, others
are performed asynchronously while or after the ioctl returns.
See the inline documentation in <linux/firewire-cdev.h> for
descriptions of all ioctls.
poll(2), select(2), epoll_wait(2) etc.
Watch for events to become available to be read.
Receive various events. There are solicited events like
outbound asynchronous transaction completion or isochronous
buffer completion, and unsolicited events such as bus resets,
request reception, or PHY packet reception. Always use a read
buffer which is large enough to receive the largest event that
could ever arrive. See <linux/firewire-cdev.h> for descriptions
of all event types and for which ioctls affect reception of
Allocate a DMA buffer for isochronous reception or transmission
and map it into the process address space. The arguments should
be used as follows: addr = NULL, length = the desired buffer
size, i.e. number of packets times size of largest packet,
prot = at least PROT_READ for reception and at least PROT_WRITE
for transmission, flags = MAP_SHARED, fd = the handle to the
/dev/fw*, offset = 0.
Isochronous reception works in packet-per-buffer fashion except
for multichannel reception which works in buffer-fill mode.
Unmap the isochronous I/O buffer from the process address space.
Besides stopping and freeing I/O contexts that were associated
with the file descriptor, back out any changes to the local
nodes' Configuration ROM. Deallocate isochronous channels and
bandwidth at the IRM that were marked for kernel-assisted
re- and deallocation.
Users: libraw1394
tools like jujuutils, fwhack, ...