RE: Linking two files together

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Mike,

Thanks for the tip. I think there may be something here I can use.

However, I am not as familiar with pipes and streams as I would like
to be.

Is it possible to use cat so the multiple files will pipe to something
that my app can open. E.g. my apps don't operate on the standard input
stream, they need to open the file, then scan back and forth within the file.

Thanks for your suggestion.

Dave Rector
*:^)


Rector, David wrote:

[snip]

> Perhaps there is a utility or wrapper that could trick any regular app
> into thinking that two files were actually one long file?

Yes, there is. It's called "cat".

cat file1 file2 file3 | your_app

Mike

________________________________________
From: Rector, David
Sent: Wednesday, May 26, 2010 10:54 AM
To: [email protected]
Subject: Re: Linking two files together

Thank you all for your quick replies,

Yes, it seems like a difficult thing to modify at the filesystem level.
Especially due to the earlier comment that the last block needs to
be filled. I hadn't considered that.

Indeed, I have many apps that need to use these files, and it would
be difficult to modify them all to look at a sequence of files. I was
looking for an easier way.

Perhaps there is a utility or wrapper that could trick any regular app
into thinking that two files were actually one long file?

Like a multiple-file soft-link?

Dave Rector
*:^)



On Wed, 2010-05-26 at 10:16 -0700, Rector, David wrote:
> It seems to me that it should be possible to simply modify the file
> entry in the filesystem such that the last inode of the first file
> points to the first inode of the second file. I guess this is similar
> to a "hard link", but used to join files rather than simply have
> another pointer to one file.

A file has one and only one inode, so that's not feasible. However the
idea of "editing" the inode contents (and the inode's blocklist or
bitmap) to make this work could be done in principle. In practice it
looks really hairy, and highly dependant on specific implementation
details of each type of filesystem. I've never heard of this being done,
but who knows?

Why do you need this? If it's for some special data-processing
application, would it not be easier to modify the app so it could
process a sequence of files?

poc


________________________________________
From: Rector, David
Sent: Wednesday, May 26, 2010 10:16 AM
To: [email protected]
Subject: Linking two files together

Hello,

I have studied various filesystems, and am fairly familiar with how they are structured. However, I am currently stuck on trying to do what seems like a simple thing.

I would like to join two files together without having to physically copy bytes (i.e. I have vary large files, so I don't want to use 'cat'). It seems to me that it should be possible to simply modify the file entry in the filesystem such that the last inode of the first file points to the first inode of the second file. I guess this is similar to a "hard link", but used to join files rather than simply have another pointer to one file.

I have seen 'mmv' and 'lxsplit' and they all seem to do the same thing, namely they want to physically copy the bytes in order to join two files together.

Is there any such utility in linux to perform such a hard link to join or connect two files together without having to copy bytes?

Thanks for your help.

Dave Rector
*:^)
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