Re: [PATCH, v3] shmat: introduce flag SHM_MAP_NOT_FIXED

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

> > Can use shm_open and mmap to get POSIX standard shm behaviour via a sane
> 
> I don't think shm_open can attach to SYSV shared segments. Or are you
> proposing to add "sysvshmfs" to make that possible? 

Actually you can do so. As it stands today the SYS3 SHM interface code
does the following

	create a char array in the form SYS%08ld, key
	open it on shmfs

> - There are legacy interfaces that cannot be really changed who use sysv shm
> (e.g. X shm and others -- just do a ipcs on your system) 

They can be changed and nobody is wanting to map those at fixed addresses.

> - An system call emulation as in qemu obviously has to implement the
> existing system call semantics.

Which it can do perfectly well using shm_open to create its SYS3
SHM objects. In fact theoertically we could bin the whole of SYS3 shm and
push it into glibc emulation if we wanted.

Alan