Re: JIT emulator needs

["Albert Cahalan" <acahalan@gmail.com>]

On 6/8/07, Eric Dumazet <dada1@cosmosbay.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.