cvs commit: src/lib/libufs type.c

[Bruce Evans]

On Fri, 16 Mar 2007, Pawel Jakub Dawidek wrote:

> On Fri, Mar 16, 2007 at 03:13:29AM +0000, Pawel Jakub Dawidek wrote:
>> pjd         2007-03-16 03:13:29 UTC
>>
>>   FreeBSD src repository
>>
>>   Modified files:
>>     lib/libufs           type.c
>>   Log:
>>   The ufs_disk_fillout(3) can take special device name (with or without /dev/
>>   prefix) as an argument and mount point path. At the end it has to find
>>   device name file system is stored on, which means when mount point path is
>>   given, it tries to look into /etc/fstab and find special device
>>   corresponding to the given mount point. This is not perfect, because it
>>   doesn't handle the case when file system is mounted by hand and mount point
>>   is given as an argument.
>>
>>   I found this problem while trying to use snapinfo(8), which passes mount
>>   ...
>
> In my opinion, when mount point is given, it should always just use
> statfs(2) and don't touch /etc/fstab, but I didn't want to change the
> current behaviour. Juli, do you have an opinion about this?

It has to look in fstab to handle the case where the file system is not
mounted.  Perhaps where it looks should be controlled by its caller.

Utilities like fsck_ffs and tunefs start with a special file name and
only care if the file system is mounted.  Then this interfaces is not
very relevant, and looking in fstab makes it less relevant.  fsck_ffs
doesn't use ufs_disk_fillout.  It searches all mount points to determine
if the special file is mounted.  tunefs uses ufs_disk_fillout() to
help get this wrong, probably in much the same way as snapinfo() (e.g.,
the cases where the file system is mounted at a point not in fstab or
at a point different from in fstab can't work without a search for the
mountpoint).

Your change doesn't add searching for the mountpoint (starting from a
special file name), so it doesn't help tunefs.  ufs_disk_fillout()
remains almost irrelevant to tunefs.  (tunefs is using it for its side
effect of mapping from the special file name (if tunefs's arg is a
special file name and not a mountpoint name to begin with) to a
mountpoint name.  Then mountedness can easily be determined by statfs()
and/or stat() on the mountpoint name followed by strcmp() of names
and/or comparison of device numbers, provided the mountpoint name is
correct if the special file is mounted.  The actual ufs disk info is
not used.)

Bruce