Add a tool to decode ioctl commands.

[jhb]

Summary

Add a tool to decode ioctl commands.

One or more ioctl command values can be passed as arguments on the command
line. For each value, the command is broken down into it's sub parts
(direction, group, number, and length). In addition, if a commands has a
known name it is output via sysdecode_ioctlname().

I've had this in my private repo for a while as a standalone little tool,
but libsysdecode integration is simpler if this is in tools/tools/ perhaps.

Sample output:

./decioctl 0xc4d01902 0xc4e01902

command :  dir  grp num len   name

0xc4d01902: INOUT 25 2 1232 CAMIOCOMMAND
0xc4e01902: INOUT 25 2 1248

Test Plan

• Run it against some constants avg@ pasted in IRC

[emaste]

tools/tools/decioctl/decioctl.c

54 ↗

(On Diff #17594)

Check for ERANGE too?

[kib]

tools/tools/decioctl/decioctl.c

81 ↗

(On Diff #17594)

Might be print both forms if the group value is printable.

[jhb]

tools/tools/decioctl/decioctl.c

54 ↗

(On Diff #17594)

Hmm, that seems like a bit of a PITA. It seems you have to explicit set errno to 0 before you call and then check errno if the return value is ULONG_MAX? Hmm, POSIX says that a successful strtol() (strtoll()) do not change errno if successful, so setting errno to 0 first and checking afterward should work in theory.

81 ↗

(On Diff #17594)

Originally it only printed '%c' since most kernel source code that I've seen uses chars for the group. Apparently CAM uses 0x19 so I added the fallback yesterday. I could print both, it just makes the layout of the table wider. I'd rather print it as hex instead of decimal anyway.

[emaste]

tools/tools/decioctl/decioctl.c

54 ↗

(On Diff #17594)

Yeah I wish there was a canonical strtol example. I think setting errno to 0 before and then checking *cp != '\0' || errno != 0 is OK for error checking.

[jhb]

• Handle errors from strtol().
• Adjust format.

[jhb]

Updated output:

> ./decioctl 0xc4d01902 0xc4e01902 0x4004667f
  command :  dir  group num  len name
0xc4d01902: INOUT  0x19   2 1232 CAMIOCOMMAND
0xc4e01902: INOUT  0x19   2 1248
0x4004667f: OUT    'f'  127    4 FIONREAD

[avg]

Looks great!