git: 443c1ab624 - main - handbook/cutting_edge: document the n-number

The branch main has been updated by imp:

URL: https://cgit.FreeBSD.org/doc/commit/?id=443c1ab6247bc5b63235cb6b52213529b3f1c6f1

commit 443c1ab6247bc5b63235cb6b52213529b3f1c6f1
Author:     Warner Losh <[email protected]>
AuthorDate: 2021-06-29 14:31:09 +0000
Commit:     Warner Losh <[email protected]>
CommitDate: 2021-06-29 19:02:44 +0000

    handbook/cutting_edge: document the n-number
    
    Document how to convert a git hash into a 'n' number. I've been asked
    this a few times and it would be good to have an easy, linkable answer.
    It seems to fit best here.
    
    Feedback from:          markj@, Pau Amma
    Reviewed by:            erj@, ceri@
    Sponsored by:           Netflix
    Differential Revision:  https://reviews.freebsd.org/D30938
---
 .../en/books/handbook/cutting-edge/_index.adoc     | 43 ++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/documentation/content/en/books/handbook/cutting-edge/_index.adoc b/documentation/content/en/books/handbook/cutting-edge/_index.adoc
index 668dabe1d9..e1b9d257bd 100644
--- a/documentation/content/en/books/handbook/cutting-edge/_index.adoc
+++ b/documentation/content/en/books/handbook/cutting-edge/_index.adoc
@@ -596,6 +596,49 @@ To compile or upgrade to an existing FreeBSD system to FreeBSD-STABLE, use `git`
 Branch names, such as `stable/9`, are listed at link:https://www.FreeBSD.org/releng/[www.freebsd.org/releng].
 . Before compiling or upgrading to FreeBSD-STABLE , read [.filename]#/usr/src/Makefile# carefully and follow the instructions in <<makeworld>>. Read the {freebsd-stable} and [.filename]#/usr/src/UPDATING# to keep up-to-date on other bootstrapping procedures that sometimes become necessary on the road to the next release.
 
+[[translate-n-number]]
+=== The N-number
+When tracking down bugs it is important to know which versions of the source code have been used to create the system exhibiting an issue.
+FreeBSD provides version information compiled into the kernel.
+man:uname[1] retrieves this information, for example:
+[source,shell]
+....
+% uname -a
+FreeBSD 14.0-CURRENT #112 main-n247514-031260d64c18: Tue Jun 22 20:43:19 MDT 2021     fred@machine:/usr/home/fred/obj/usr/home/fred/git/head/amd64.amd64/sys/FRED
+....
+Looking at the 4th field, it is made up of several parts:
+[source,shell]
+....
+main-n247514-031260d64c18
+
+main		<.>
+n247514		<.>
+031260d64c18	<.>
+....
+<.> Git branch name.
+Note: comparisons of n-numbers are only valid on branches published by the project (`main`, `stable/XX` and `releng/XX`).
+Local branches will have n-numbers that will overlap commits of their parent branch.
+<.> The n-number is a linear count of commits back to the start of the Git repository starting with the Git hash included in the line.
+<.> Git hash of the checked out tree
+<.> Sometimes a suffix of `-dirty` is present when the kernel was built in a tree with uncommitted changes.
+It is absent in this example because the FRED kernel was built from a pristine checkout.
+
+The `git rev-list` command is used to find the n-number corresponding to a Git hash.
+For example:
+[source,shell]
+....
+% git rev-list --first-parent --count 031260d64c18 <.>
+247514 <.>
+....
+<.> git hash to translate (the hash from the above example is reused)
+<.> The n-number.
+
+Usually this number is not all that important.
+However, when bug fixes are committed, this number makes it easy to quickly determine whether the fix is present in the currently running system.
+Developers will often refer to the hash of the commit (or provide a URL which has that hash), but not the n-number since the hash is the easily visible identifier for a change while the n-number is not.
+Security advisories and errata notices will also note an n-number, which can be directly compared against your system.
+When you need to use shallow Git clones, you cannot compare n-numbers reliably as the `git rev-list` command counts all the revisions in the repository which a shallow clone omits.
+
 [[makeworld]]
 == Updating FreeBSD from Source
 
_______________________________________________
[email protected] mailing list
https://lists.freebsd.org/mailman/listinfo/dev-commits-doc-all
To unsubscribe, send any mail to "[email protected]"