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# 6. Adventures in ioctl(2) Support

- See ioctl_list(2)

## 6.1 Decoding Request Numbers

- first impression: large but limited set
- switch: they don't play well together
  one ioctl handler per source file
- reality: private request numbers
- ambiguity: private and historical (look at file descriptor)
- internal table of pointers (not a problem yet); slide
- ...each has optional "method" to disambiguate
- URL.. follow along the source code

## 6.2 Representation

- "fildes" is handled the same way as the other system calls
- "request" is handled on previous slide
- accurate representation of 3rd argument; slide
- ...each ioctl request has "method" to print data
- ...output-only requests just print the pointer

## 6.3 Explanations

- each ioctl request has "method" to print explanation; slide
- set set of errno(3) value usually not documented
- this is where you read kernel source

## 6.4 EINVAL vs ENOTTY

- like system calls, this is messy; slide
- kernel source comments indicate this may be being dealt with
- also: ENOSYS, ENOTSUP EOPNOTSUP, and (not Linux) ENOIOCTL

## 6.5 intptr_t

- shoe-horn
- prototype; slide
- ...bye bye type safety
- tcflush(3) and friends
- [e]glibc internally: two ways
- sys_ioctl
- cognitive dissonance = bugs
- intptr_t