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SubjectRe: 2.3.51-52.pre1, shm and mounting somewhere else than /var/shm...
Date
Christoph Rohland writes:
> "Albert D. Cahalan" <acahalan@cs.uml.edu> writes:

>> Documentation doesn't a feature make. It seems odd that the kernel
>> would not know where a filesystem is mounted. The kernel, more than
>> anything else, ought to be aware of filesystem mount points.
>
> My first version had this feature, but it was an ugly hack and I did
> not find a way to reliably export this to user space without further
> hacks.

Going to user space you have /proc/mounts and /etc/mtab.

> Unfortunately the fs does not get the mount point from anywhere. The
> only function called by the VFS ist read_super, which does not get the
> information. If you want to autodetect, you have to play tricks with
> dcache and the path to your root inode.

a. play tricks
b. change read_super

>> BTW, /var/shm is a bad default. Stuff like this should be right on
>> the root because /var may be a separate filesystem that gets mounted
>> after the system already needs shared memory.
>
> I am very open to proposals for other mount point defaults. But
> personally I really do not like any further root directory cluttering.

Stuff that belongs on the root: historical requirements, mount
points for special filesystems, and locally desired junk.
Instead of "clutter", think "short and fast paths".

> Another idea would be /dev/shm like /dev/pts but I wanted to avoid
> clashes with devfs.

There isn't a clash, but this adds a mount order dependency.
It would mean the shm filesystem can not be mounted until
after devfs (or /var in the current code) has successfully
been mounted. Going the other direction, a hung shm filesystem
would prevent /dev or /var from being unmounted.

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