Re: JIT emulator needs

From: Albert Cahalan
Date: Sat Jun 09 2007 - 00:12:41 EST

On 6/8/07, Eric Dumazet <dada1@xxxxxxxxxxxxx> 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 ?)


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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