bsdinstall: fix prepopulating the ZFS disk menu with ZFSBOOT_DISKS

[dteske]

Summary

If the ZFSBOOT_DISKS variable is set to one or more disk names, then
those disks should be preselected in the disk menu. However, the code
wasn't correctly setting the variable, leaving all disks unselected.

MFC after: 2 weeks
Sponsored by: Axcient

Test Plan

manually tested

[dteske]

The change to use f_isset in 2 places is a good one, thank you. However, I have issue with the removal of the call to "local" above the second hunk.

usr.sbin/bsdinstall/scripts/zfsboot

670–672

As the comment states above this block, "create temporary locals"

The "f_isset ... || local ..." should remain (and not be removed) while I do agree with the latter part of fixing the ...=... to use setvar since it requires indirection to set.

[asomers]

• Restore local variable declaration

[dteske]

Looks good

[dteske]

Do you need me to commit this or do you have a venue/access?

[asomers]

In D35331#800920, @dteske wrote:

Do you need me to commit this or do you have a venue/access?

I'll commit it myself. Thanks for the prompt review.

[dteske]

This is not what I wanted. The second diff (that I prematurely accepted) that you committed omits the f_isset call

[dteske]

usr.sbin/bsdinstall/scripts/zfsboot

670–673

This is not correct.

This introduces a memory leak. I am sorry that I approved it, and that was premature. I thought you had committed my suggestion which retains the f_isset test.

The fact is, that "local" should NEVER be used to declare-local a variable that is already local because it leaks memory.

I had not realized you removed the f_isset before I approved.

[dteske]

Fix a memory leak introduced by previous commit.

[asomers]

Oh, sorry about that. I'll commit the fix. I didn't even realize that it was possible to leak memory in sh.

[dteske]

In D35331#801282, @asomers wrote:

Oh, sorry about that. I'll commit the fix. I didn't even realize that it was possible to leak memory in sh.

Thank you so much.

The quickest way to see this memory leak in action is to:

1. Execute top, press "o", type "size", press ENTER (to sort on SIZE column)
2. In another shell, execute: sh -c '_(){ while :;do local a; done; };_'
3. Observe the SIZE column as the "sh" rises to the top
4. Press Ctrl-C to kill the sh