Memory disk "a la mfsroot"?
pldrouin at pldrouin.net
Thu Feb 11 17:10:50 UTC 2010
Matthew Seaman wrote:
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> On 11/02/2010 15:39, RW wrote:
>> On Thu, 11 Feb 2010 15:12:22 +0000
>> Matthew Seaman <m.seaman at infracaninophile.co.uk> wrote:
>>> On 11/02/2010 14:53, Pierre-Luc Drouin wrote:
>>>> I would like to know if there is a mount command that allows to
>>>> create a memory disk that can be initialized from a file. What I am
>>>> looking for is something like mount_mfs -F, but that does not
>>>> modify the actual file. I know what I could easily to this by
>>>> copying the content of the file to the memory disk, but I am
>>>> looking for a solution that can be configured via fstab.
>>> Yes. See mdconfig(8) -- there are examples in there of exactly what
>>> you want to do.
>> I don't think covers what he is asking for. I think you would need a
>> union filsystem that overlays a swap-backed filesystem on top of a
>> file-backed filesystem - if that's possible.
> Actually, I was thinking more along the lines of mounting a .iso as a
> cd9660 filesystem. Which won't muck up the underlying .iso, but only
> because it's read-only. You could mount a FFS image read-only in
> exactly the same way -- I think there's a 'last mounted on' field in the
> backing file image that will be updated if the it is writable (even if
> the fs itself is mounted ro) but that's not the right answer either.
> Basically, you're going to have to mount and initialise as two separate
> operations as far as I can see.
By this do you mean that I would need to copy the whole content of the
read-only filesystem to the memory disk?
I looked at the man page for mount_unionfs and there is a big warning
saying that it is a bad idea to use it, so I guess I will pass on this
What I am trying to do basically is to mount a filesystem from a CD but
I want to use a memory disk to allow write operations. I would basically
want the filesystem to behave like a regular read-write filesystem, but
not have to copy everything into a memory disk. What does "mfs_root" do
exactly in the official FreeBSD boot CDs? Does it copy the content of
mfsroot.gz into a memory disk? That filesystem is so small that I guess
it can be copied without any problem...
> - --
> Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
> Flat 3
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> Kent, CT11 9PW
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