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Diffstat (limited to 'Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg')
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diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg new file mode 100644 index 000000000000..e9e58d4ea60a --- /dev/null +++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg @@ -0,0 +1,58 @@ +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. |