Hi Bruce, thanks for the input! I will see if I can move that piece into loader.8 and extend it a bit from the source "documentation".
-Max On Thu, Apr 7, 2016 at 8:38 PM, Bruce Evans <b...@optusnet.com.au> wrote: > On Fri, 8 Apr 2016, Maxim Sobolev wrote: > > Log: >> Document vfs.root.mountfrom. >> >> Reviewed by: imp, wblock >> > > The format of this variable is still undocumented, except in the source > code. > > Modified: head/sys/boot/forth/loader.conf.5 >> >> ============================================================================== >> --- head/sys/boot/forth/loader.conf.5 Fri Apr 8 00:01:19 2016 >> (r297689) >> +++ head/sys/boot/forth/loader.conf.5 Fri Apr 8 00:24:21 2016 >> (r297690) >> > > This variable is (partly) documented in a different wrong file than the > source file. It isn't a loader option. It is a kernel tunable. No > other kernel tunables are documented in loader.conf.5. Some of them are > documented in loader.8 (not really the right place --- loader is just 1 > way of setting them, and isn't a way of reading or interpreting them). > loader.8 also documents most loader options as BUILTIN ENVIRONMENT > VARIABLES. It does this much better than loader.conf.5. It documents > 30 such options and only has a couple of ordering errors in the list, > whie loader.conf.5 documents 15 such options in random order. About > half of the 15 are in both, and their descriptions give quite different > details in a quite different style (too much double quoting in > loader.conf.5). loader.8 documents only 16 tunables, with more ordering > errors that for options. > > @@ -112,6 +112,31 @@ The name must be a subdirectory of >> that contains a kernel. >> .It Ar kernel_options >> Flags to be passed to the kernel. >> +.It Ar vfs.root.mountfrom >> +Specify the root partition to mount. >> +For example: >> +.Pp >> +.Dl vfs.root.mountfrom="ufs:/dev/da0s1a" >> > > The source code gives the details needed to actually use this variable > without guessing from a single example. It gives both an informal and > formal description: > > X /* > X * The root filesystem is detailed in the kernel environment variable > X * vfs.root.mountfrom, which is expected to be in the general format > X * > X * <vfsname>:[<path>][ <vfsname>:[<path>] ...] > X * vfsname := the name of a VFS known to the kernel and capable > X * of being mounted as root > X * path := disk device name or other data used by the filesystem > X * to locate its physical store > X * > X * If the environment variable vfs.root.mountfrom is a space separated > list, > X * each list element is tried in turn and the root filesystem will be > mounted > X * from the first one that suceeds. > X * > X * The environment variable vfs.root.mountfrom.options is a comma > delimited > X * set of string mount options. These mount options must be parseable > X * by nmount() in the kernel. > X */ > > I thought that these careful descriptions were broken using sbufs which > accidentally (?) changed the separator from space to newline. However, > I can' find any trace of this in my config files -- they now just use > a space. I might have just been confused by old kernels not supporting > lists. > > I mainly use this feaature to work around the renaming of ad to ada and > loss of the compatibility support for this. My lists look like > "ufs:ad4s3a ufs:ada0s3a ufs:ad0s2a". Old kernels don't support lists, > but they also don't support ada; they use the first entry and this works > although the documentation says it shouldn't (the comment says that > the format is <vfsname>:[<path>] and doesn't mention field separators or > trailing garbage). FreeBSD-11 doesn't supprt ad, but it supports lists; > so it uses the second entry. This works on 2 systems with similar disk > numbering. The third entry is for another system with different disk > numbering an no ad4. This almost never works -- with old kernels, the > list doesn't work, and with new kernels the list works and ada0 exists > and ada0s3a exists, but it is not the right boot partition. This works > with intermediate kernels with lists but no ada0, so that the third > entry is used. > > Bruce > > _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
