1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
What: /sys/firmware/qemu_fw_cfg/
Date: August 2015
Contact: Gabriel Somlo <somlo@cmu.edu>
Description:
Several different architectures supported by QEMU (x86, arm,
sun4*, ppc/mac) are provisioned with a firmware configuration
(fw_cfg) device, originally intended as a way for the host to
provide configuration data to the guest firmware. Starting
with QEMU v2.4, arbitrary fw_cfg file entries may be specified
by the user on the command line, which makes fw_cfg additionally
useful as an out-of-band, asynchronous mechanism for providing
configuration data to the guest userspace.
The authoritative guest-side hardware interface documentation
to the fw_cfg device can be found in "docs/specs/fw_cfg.txt"
in the QEMU source tree.
=== SysFS fw_cfg Interface ===
The fw_cfg sysfs interface described in this document is only
intended to display discoverable blobs (i.e., those registered
with the file directory), as there is no way to determine the
presence or size of "legacy" blobs (with selector keys between
0x0002 and 0x0018) programmatically.
All fw_cfg information is shown under:
/sys/firmware/qemu_fw_cfg/
The only legacy blob displayed is the fw_cfg device revision:
/sys/firmware/qemu_fw_cfg/rev
--- Discoverable fw_cfg blobs by selector key ---
All discoverable blobs listed in the fw_cfg file directory are
displayed as entries named after their unique selector key
value, e.g.:
/sys/firmware/qemu_fw_cfg/by_key/32
/sys/firmware/qemu_fw_cfg/by_key/33
/sys/firmware/qemu_fw_cfg/by_key/34
...
Each such fw_cfg sysfs entry has the following values exported
as attributes:
name : The 56-byte nul-terminated ASCII string used as the
blob's 'file name' in the fw_cfg directory.
size : The length of the blob, as given in the fw_cfg
directory.
key : The value of the blob's selector key as given in the
fw_cfg directory. This value is the same as used in
the parent directory name.
raw : The raw bytes of the blob, obtained by selecting the
entry via the control register, and reading a number
of bytes equal to the blob size from the data
register.
|
