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From: Bharath Vedartham <>
To: "Valdis Klētnieks" <>
Subject: Re: Overwriting copy functionality in filesystem
Date: Sun, 24 Mar 2019 18:48:08 +0530
Message-ID: <20190324131808.GA24735@bharath12345-Inspiron-5559> (raw)
In-Reply-To: <13539.1553367716@turing-police>

On Sat, Mar 23, 2019 at 03:01:56PM -0400, Valdis Klētnieks wrote:
> On Sat, 23 Mar 2019 22:29:45 +0530, Bharath Vedartham said:
> > I was wondering how we can overwrite the copy functionality while
> > writing our own filesystem in linux. 
> > VFS does not offer any sort of API for copy. I think it calls create and
> > write when we execute the copy the file/dir.
> Which you can verify using strace.  Which you should already be familiar with
> if you have the experience needed to write a usable filesystem.
Yes I did that. I have observed that it is a mixture of
create,read,write system calls.
> > I am interested in overwriting the way copy happens in my
> > filesystem(which I am writing for fun :p). 
> And what, exactly, do you want copy to do differently on the API level,
> and on the file system level?
I was interested in implementing copy-on-write for my filesystem(for fun
:P). When I do a "cp" operation, I do not want to create a seperate
inode for the new file. I only want to create a inode when I make a
change to the file. 

There is no vfs api for cp. I would need to make creat syscall aware of the
fact that it is being executed by "cp". My immediate idea was to check
if a file with the same data exists in the filesystem but that would be
way too much overhead.

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Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-23 16:59 Bharath Vedartham
2019-03-23 19:01 ` Valdis Klētnieks
2019-03-24 13:18   ` Bharath Vedartham [this message]
2019-03-24 14:06     ` Valdis Klētnieks
2019-03-28 18:30       ` Bharath Vedartham
2019-03-28 20:07         ` Valdis Klētnieks
2019-03-23 19:03 ` Bernd Petrovitsch
2019-03-24 13:21   ` Bharath Vedartham
2019-03-23 19:05 ` Greg KH

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