Allow platform dependent path stripping for vdevs

[ghost]

Motivation and Context

On Linux the full path preceding devices is stripped when formatting vdev names. On FreeBSD we only want to strip "/dev/".

Description

Hide the implementation details of path stripping behind zfs_strip_path().

Make zfs_strip_partition_path() static in Linux implementation while here, since it is never used outside of the file it is defined in. Some reordering was performed to logically group function definitions before use in the file after removing the forward declaration.

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.

[codecov]

Codecov Report

Merging #9565 into master will increase coverage by 0.09%.
The diff coverage is 90.62%.

@@            Coverage Diff             @@
##           master    #9565      +/-   ##
==========================================
+ Coverage   79.16%   79.26%   +0.09%     
==========================================
  Files         418      418              
  Lines      123686   123687       +1     
==========================================
+ Hits        97917    98039     +122     
+ Misses      25769    25648     -121

Flag	Coverage Δ
#kernel	79.74% <ø> (+0.06%)	⬆️
#user	67.37% <90.62%> (+0.31%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 734de7c...98af872. Read the comment docs.

[ghost]

can we simply unify how they show device paths so all platforms behave consistently

I don't think so. Each platform has very different device naming practices to account for. Portions of the path after /dev/ are important to display on FreeBSD, for example to differentiate /dev/mirror/foo from /dev/label/foo or /dev/gpt/foo. On Linux I believe a conscious decision was made to shorten the display name for formatting purposes due to the common use of longer names such as /dev/disk/by-path/pci-000:00:1f.2-ata-4.0-part1 or /dev/disk/by-partuuid/9d1dba85-f82a-4025-943d-797e4096e386. On illumos a different approach is required as well. Letting each platform handle its particular needs separately makes sense.

[behlendorf]

While I agree that it might be nice in principle to have a common implementation, practically speaking this is one area where the platforms are significantly different. Letting each platform provide its own functions for this is very reasonable, and not that much code.