Output file name from "preload" type md(4) device

[stevek]

Summary

For MD_PRELOAD type md(4) devices, if there is a file name in the preloaded
meta-data, copy it into the softc structure.

When returning md(4) device details to the caller, include the file name in
any MD_PRELOAD type devices if it is set (first character is not NUL.)

In mdconfig, for "preload" type md(4) devices, if there is file config
available, print it in the file column of the output.

Test Plan

Built and tested on x86 and ARM by pre-loading ISO images from the loader and
checking mdconfig output. Also created other md types to ensure output from
mdconfig looks correct.

[brooks]

Looks good to me.

sys/dev/md/md.c

1694 ↗

(On Diff #24970)

Not new in your code, but this case is awful. It does does a copyout to the buffer and just hopes it's at least PATH_MAX.

[stevek]

sys/dev/md/md.c

1694 ↗

(On Diff #24970)

yes, the problem is the md_ioctl structure does not have a size for the md_file member and it really should.