Add support for backing up the old kernel when installing a new kernel

using freebsd-update.  This applies to using freebsd-update in "upgrade
mode" and normal freebsd-update on a security branch.

The backup kernel will be written to /boot/kernel.old, if the directory
does not exist, or the directory was created by freebsd-update in a
previous backup.  Otherwise freebsd-update will generate a new directory
name for use by the backup.  By default symbol files are not backed up
to save diskspace and avoid filling up the root partition.

This feature is fully configurable in the freebsd-update config file,
but defaults to enabled.

MFC after:	1 week (stable/7)
Reviewed by:	cperciva
Approved by:	re (kib)

1 files changed, 50 insertions, 2 deletions

diff --git a/share/man/man5/freebsd-update.conf.5 b/share/man/man5/freebsd-update.conf.5
index 29775fd..d372102 100644
--- a/share/man/man5/freebsd-update.conf.5
+++ b/share/man/man5/freebsd-update.conf.5
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 30, 2006
+.Dd August 19, 2009
 .Dt FREEBSD-UPDATE.CONF 5
 .Os FreeBSD
 .Sh NAME
@@ -48,7 +48,7 @@ error.
 .Pp
 The possible options and their meanings are as follows:
 .Pp
-.Bl -tag -width "KeepModifiedMetadata"
+.Bl -tag -width ".Cm BackupKernelSymbolFiles"
 .It Cm KeyPrint
 The single parameter following this keyword is the SHA256 hash
 of the RSA key which will be trusted to sign updates.
@@ -171,6 +171,54 @@ command is used ("yes"), or merely as a list of components
 which might be installed, of which
 .Cm freebsd-update
 should identify which in fact are present ("no").
+.It Cm BackupKernel
+The single parameter following this keyword must be
+.Dq yes
+or
+.Dq no
+and specifies whether
+.Cm freebsd-update
+will create a backup of the old kernel before installing a new kernel.
+This backup kernel can be used to recover a system where the newly
+installed kernel somehow did not work.
+Note that the backup kernel is not reverted to its original state by
+the
+.Cm freebsd-update
+rollback command.
+.It Cm BackupKernelDir
+This keyword sets the directory which is used to store a backup
+kernel, if the BackupKernel feature is enabled.
+If the directory already exist, and it was not created by
+.Cm freebsd-update ,
+the directory is skipped.
+In the case of the primary directory name not being usable, a number
+starting with
+.Sq 1
+is appended to the directory name.
+Like with the primary directory name, the constructed directory name is
+only used if the path name does not exist, or if the directory was
+previously created by
+.Cm freebsd-update .
+If the constructed directory still exist the appended number is
+incremented with 1 and the directory search process restarted.
+Should the number increment go above 9,
+.Cm freebsd-update
+will abort.
+.It Cm BackupKernelSymbolFiles
+The single parameter following this keyword must be
+.Dq yes
+or
+.Dq no
+and specifies whether
+.Cm freebsd-update
+will also backup kernel symbol files, if they exist.
+The kernel symbol files takes up a lot of disk space and are not
+needed for recovery purposes.
+If the symbol files are needed, after recovering a system using the
+backup kernel, the
+.Cm freebsd-update
+rollback command will recreate the symbol files along with the old
+kernel.
 .El
 .Sh FILES
 .Bl -tag -width "/etc/freebsd-update.conf"