Date: Sat, 18 Nov 1995 14:26:30 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: grog@lemis.de Cc: terry@lambert.org, hackers@freebsd.org Subject: Re: elm problem - "solved" Message-ID: <199511182126.OAA09612@phaeton.artisoft.com> In-Reply-To: <199511180800.JAA16684@allegro.lemis.de> from "Greg Lehey" at Nov 18, 95 09:00:08 am
next in thread | previous in thread | raw e-mail | index | archive | help
> > > /*
> > > * Advisory file segment locking data type -
> > > * information passed to system by user
> > > */
> > > struct flock {
> > > short l_type; /* lock type: read/write, etc. */
> > > short l_whence; /* type of l_start */
> > > off_t l_start; /* starting offset */
> > > off_t l_len; /* len = 0 means until end of file */
> > > pid_t l_pid; /* lock owner */
> > > };
> >
> > BZZZT. SunOS4 has the syspid as well. It's necessary for NFS locking,
> > which is why my NFS locking kernel support patches had it as well.
>
> OK, here's the extract from my SunOS 4.1.3_U1B man page:
>
> The record to be locked or unlocked is described by the
> flock structure defined in <fcntl.h> as follows:
>
> struct flock {
> short l_type; /* F_RDLCK, F_WRLCK, or F_UNLCK */
> short l_whence; /* flag to choose starting offset */
> long l_start; /* relative offset, in bytes */
> long l_len; /* length, in bytes; 0 means lock to EOF */
> pid_t l_pid; /* returned with F_GETLK */
> };
>
> In <sys/fcntlcom.h>, the definition is:
>
> /* file segment locking set data type - information passed to system by user */
> struct flock {
> short l_type; /* F_RDLCK, F_WRLCK, or F_UNLCK */
> short l_whence; /* flag to choose starting offset */
> long l_start; /* relative offset, in bytes */
> long l_len; /* length, in bytes; 0 means lock to EOF */
> short l_pid; /* returned with F_GETLK */
> short l_xxx; /* reserved for future use */
> };
#ifndef _POSIX_SOURCE
/* extended file segment locking set data type */
struct eflock {
short l_type; /* F_RDLCK, F_WRLCK, or F_UNLCK */
short l_whence; /* flag to choose starting offset */
long l_start; /* relative offset, in bytes */
long l_len; /* length, in bytes; 0 means lock to EOF */
short l_pid; /* returned with F_GETLK */
short l_xxx; /* reserved for future use */
long l_rpid; /* Remote process id wanting this lock */
long l_rsys; /* Remote system id wanting this lock */
};
#endif /* !_POSIX_SOURCE */
I have access to a SunOS 4.1.3 box as well. 8-).
> So yes, maybe l_xxx is used as a syspid. But I don't think so, and
> it's certainly not documented.
Yeah. NFS locking isn't documented. So? Here's some "close" doc:
% man fcntl
[ ... ]
F_RSETLK
F_RSETLKW
F_RGETLK Are used by the network lock daemon,
lockd(8C), to communicate with the NFS server
kernel to handle locks on the NFS files.
[ ... ]
Also not documented:
F_CNVT Convert an NFS file handle to an fd for the
rpc.lockd process.
F_UNLKSYS Remove all locks by remote system id (l_rsys).
The kernel code for NFS locking is actually pretty damn obvious, with
the exception of function callback registration in the NFS init code
to let F_CNVT work when NFS is an LKM. 8-).
> > > I really have great difficulty understanding why this change was made.
> > > It means that old FreeBSD and BSD/386 binaries won't work correctly
> > > under FreeBSD or BSD/OS Versions 2. I can't see any advantage at all
> > > in this change. Grrrr.
> >
> > Think packing on RISC systems. You put the largest followed by the
> > smallest to reduce the copyin overhead.
>
> Think reality. short=2 bytes. long=4 bytes for all the systems we're
> talking about. The only 8-byte constraint in most RISC systems is for
> doubles on the Sparc architecture--I don't know for sure for other
> RISCs. Can you point to more restrictive constraints?
>From stdio.h:
==========================================================================
/*
* This is fairly grotesque, but pure ANSI code must not inspect the
* innards of an fpos_t anyway. The library internally uses off_t,
* which we assume is exactly as big as eight chars. (When we switch
* to gcc 2.4 we will use __attribute__ here.)
*
* WARNING: the alignment constraints on an off_t and the struct below
* differ on (e.g.) the SPARC. Hence, the placement of an fpos_t object
* in a structure will change if fpos_t's are not aligned on 8-byte
* boundaries. THIS IS A CROCK, but for now there is no way around it.
*/
==========================================================================
(BTW: we're after gcc 2.4: where is __attribute__? 8-)).
off_t is 8 bytes. It's a quad. Check the GCC configuration file for
"quad" and/or "long long".
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199511182126.OAA09612>