efivar: support device paths as well as mounted paths in path_to_dp

[imp]

Summary

In path_to_dp, allow passing in either the actual device path "eg
/dev/foo/bar" or the path where the device is mounted (say
/mnt/baz/bing). In the former case we'll assume the path within the
device is nothing (the relpath). In the latter, we'll take from the
mount point on down as the relpath.

Sponsored by: Netflix

[asomers]

Is the purpose of this change to accept either a "/dev/foo/bar" or a "foo/bar"? Also, in your commit message could you check the word choice in "know the path passed in" ?

[imp]

In D38616#878885, @asomers wrote:

Is the purpose of this change to accept either a "/dev/foo/bar" or a "foo/bar"? Also, in your commit message could you check the word choice in "know the path passed in" ?

Not quite. The purpose of the change is to allow either /dev/foo/bar or /mnt/baz to be passed in.

I'll update the proposed commit message to see if my second attempt is any clearer.

[asomers]

lib/libefivar/efivar-dp-xlate.c

650–651

This comment is now out of date.

[imp]

Update per review