Date: Mon, 05 May 2003 16:53:26 +0100 From: Ian Dowse <iedowse@maths.tcd.ie> To: Martin Blapp <mbr@FreeBSD.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/compat/linux linux_ipc.c src/sys/sys syscallsubr.h src/sys/kern sysv_shm.c Message-ID: <200305051653.aa98706@salmon.maths.tcd.ie> In-Reply-To: Your message of "Mon, 05 May 2003 02:22:58 PDT." <200305050922.h459Mwdu049419@repoman.freebsd.org>
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In message <200305050922.h459Mwdu049419@repoman.freebsd.org>, Martin Blapp writ
es:
> Change the semantics of sysv shm emulation to take a additional
> argument to the functions shm{at,ctl}1 and shm_find_segment_by_shmid{x}.
> The BSD semantics didn't allow the usage of shared segment after
> being marked for removal through IPC_RMID.
I had a few incomplete stack-gap patches in this area, so I was
just looking over this change while merging. The shmctl() system
call is unfortunately quite messy to deal with, since its `struct
shmid_ds *buf' argument can point at a different type of structure
(struct shm_info) for some commands. BTW, it seems that these
additional commands (IPC_INFO, SHM_INFO) and also SHM_STAT are not
documented in shmctl(2) so they really only exist for use by the
Linux emulator.
A few comments about these changes:
- shmctl() now assumes that it can fit a `struct shm_info' into
`struct shmid_ds buf'. While it does fit now, it would be much
better to use a union so as not to need this assumption.
- The `bufsz' argument to kern_shmctl() seems to be unnecessary,
since callers are required to know already how much space is
required - they supplied that space. It would be better just to
have shmctl() switch on the command code and then copyout
sizeof(struct shm_info) or sizeof(struct shm_info) accordingly.
- Is the 'if (error) {td->td_retval[0] = -1;}' at the end of shmctl()
really necessary? The syscall() code should ignore td->td_retval[0]
in the error case.
Ian
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