linux-kernel - Re: JIT emulator needs

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Message-ID: <787b0d920706082112v25fb118ew3556eb868c118c1c@mail.gmail.com>
Date:	Sat, 9 Jun 2007 00:12:25 -0400
From:	"Albert Cahalan" <acahalan@...il.com>
To:	"Eric Dumazet" <dada1@...mosbay.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	"Davide Libenzi" <davidel@...ilserver.org>
Subject: Re: JIT emulator needs

On 6/8/07, Eric Dumazet <dada1@...mosbay.com> wrote:
> Albert Cahalan a écrit :

> > Additions to better support JIT emulators:
> >
> > a. sysctl to set IPC_RMID by default
>
> Not very good, this will break some apps.

As a sysctl, the admin gets to choose between
compatibility and sanity.

I can see such a sysctl also being really helpful for a
shared computer used for an Operating Systems or
System Programming course.

> > b. shmget() flag to set IPC_RMID by default
>
> This is better :)

Both are good. This one requires that all apps using
SysV shared memory be modified to use the flag.
The other requires that a very few apps be modified
to tolerate a behavior change.

> > c. open() flag to unlink a file before returning the fd
>
>
> Well, I assume you would like fd = open("/path/somefile", O_RDWR | O_CREAT |
> O_UNLINK, 0644)
>
> (ie allocate a file handle but no name ?)

Yes.

> Quite difficult to implement this atomically with current vfs, maybe a new
> syscall would be better. (Linus will kill me for that :) )
>
> (We dont need to insert "somefile" in one directory, then unlink it, we only
> need to allocate an unnamed inode to get some backing store)

I suspect that SMB/CIFS has a native call for this. There is
some sort of tmpfile flag defined over in that world.
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