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Re: File real location

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notbob wrote:

> On 2011-04-26, The Natural Philosopher <tnp@invalid.invalid> wrote:
>> Richard Kettlewell wrote:
>>> JimR <NotReallyMyEmail@example.net> writes:
> 
>>>> Now I create a file on it, let's call it bar.  Now I have
>>>> /foo/bar
>>>>
>>>> In an alternative case, the filesystem is not mounted.  I can still
>>>> create a file bar in the directory foo, but it will fall onto the
>>>> default filesystem (likely root filesystem).
>>>>
>>>> How can I tell the difference between these 2 files, i.e., on which
>>>> filesystem did the file land?
>>> 
>>> stat() it and look at st_dev.
>>> 
>> I bow to a superior solution...
> 
> 
> Ummm.... let's back up a bit.  Nevermind I haven't a clue what stat()
> and st_dev are. 

man -S2 stat

returns a lot of what there is to know about a file/devicenode/other 
including size, timestamps, owner and st_dev which is the block device the 
file lives on. It doesn't matter for the question here what the actual 
st_dev numbers are - only whether they are the same (same block device ie 
same disk/partition) or different.

> If a "filesystem is not mounted", how could there be
> any root (/) dir?  

There's (almost) always at least one filesystem mounted and that is / (even 
if the mount is a fudge from a packed special file or embedded in the 
kernel).

Every mount *must* happen on an existing directory - so if there is no 
filesystem mounted on /x/y/z/ and you stick a file in /x/y/z/ then the file 
lives in the filesystem that z/ is a member of which may or may not be the 
FS that / is from. If you mount another FS on /x/y/z/ and the stick a file 
in z/ then the file exists on the FS you just mounted there.

> If the dir foo has not been mounted how can one put
> a file into a dir that doesn't exist ...in a filesystem that hasn't
> been mounted?  Is there some editor ....cat, vi, emacs... that will
> create a filesystem and dir if a nonexistent dir/file is specified and
> doesn't exist?

Sometimes. There are tools that allow (v)fat/msdos filesystem devices to be 
manipulated without mounting. In principle you can manipulate any raw device 
to add a file to its contained FS if any - whether there was any point to 
anyone writing such a tool is another matter altogether.

If you are hard core, you could use hexedit on any FS device - but you would 
have to intimately know the data structures involved such as free 
block/extent lists, directory structures, inode structures and more.

HTH

Tim

-- 
Tim Watts

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Thread

File real location JimR <NotReallyMyEmail@example.net> - 2011-04-26 13:06 -0400
  Re: File real location Richard Kettlewell <rjk@greenend.org.uk> - 2011-04-26 18:24 +0100
    Re: File real location The Natural Philosopher <tnp@invalid.invalid> - 2011-04-26 18:28 +0100
      Re: File real location notbob <notbob@notbob.invalid> - 2011-04-26 18:08 +0000
        Re: File real location Richard Kettlewell <rjk@greenend.org.uk> - 2011-04-26 19:14 +0100
        Re: File real location Tim Watts <tw@dionic.net> - 2011-04-26 19:25 +0100
        Re: File real location unruh <unruh@wormhole.physics.ubc.ca> - 2011-04-26 18:43 +0000
        Re: File real location Chris Davies <chris-usenet@roaima.co.uk> - 2011-04-27 16:31 +0100
    Re: File real location Tim Watts <tw@dionic.net> - 2011-04-26 19:08 +0100
    Re: File real location JimR <NotReallyMyEmail@example.net> - 2011-04-26 14:43 -0400
      Re: File real location Richard Kettlewell <rjk@greenend.org.uk> - 2011-04-26 20:28 +0100
        Re: File real location JimR <NotReallyMyEmail@example.net> - 2011-04-26 17:00 -0400
  Re: File real location The Natural Philosopher <tnp@invalid.invalid> - 2011-04-26 18:27 +0100
  Re: File real location "Chris F.A. Johnson" <cfajohnson@gmail.com> - 2011-04-26 13:44 -0400
  Re: File real location unruh <unruh@wormhole.physics.ubc.ca> - 2011-04-26 17:52 +0000

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