Date: Wed, 21 Feb 2001 12:37:06 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: John Baldwin <jhb@FreeBSD.org>, "Pierre Y. Dampure" <pierre.dampure@westmarsh.com>, cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/sys user.h Message-ID: <Pine.BSF.4.21.0102211220350.24536-100000@besplex.bde.org> In-Reply-To: <95465.982704647@critter>
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On Tue, 20 Feb 2001, Poul-Henning Kamp wrote:
> I think that a simple version number will be sufficient and that a sizeof
> will be convenient. I don't think the sizeof should be a #define like
> now, but rather an actual sizeof().
>
> The current #define SIZEOF is unlikely to work on Bruce's i386/64bit-long
> kernel for instance.
sizeof() on the whole struct doesn't work because it is the size of the
whole struct (and layout of the used parts).
I use the following to fix a related problem (and some tab lossage)
in struct statfs:
---
diff -c2 mount.h~ mount.h
*** mount.h~ Tue Feb 20 01:18:48 2001
--- mount.h Tue Feb 20 01:18:51 2001
***************
*** 63,73 ****
#define MFSNAMELEN 16 /* length of fs type name, including null */
! #ifdef __i386__
! #define MNAMELEN 80 /* length of buffer for returned name */
! #endif
! #if defined(__alpha__) || defined(__ia64__)
! #define MNAMELEN 72 /* length of buffer for returned name */
! #endif
struct statfs {
long f_spare2; /* placeholder */
--- 63,70 ----
#define MFSNAMELEN 16 /* length of fs type name, including null */
! #define MNAMELEN (88 - 2 * sizeof(long)) /* size of on/from name bufs */
+ /* XXX getfsstat.2 is out of date with write and read counter changes here. */
+ /* XXX statfs.2 is out of date with read counter changes here. */
struct statfs {
long f_spare2; /* placeholder */
***************
*** 83,96 ****
int f_type; /* type of filesystem */
int f_flags; /* copy of mount exported flags */
! long f_syncwrites; /* count of sync writes since mount */
! long f_asyncwrites; /* count of async writes since mount */
char f_fstypename[MFSNAMELEN]; /* fs type name */
char f_mntonname[MNAMELEN]; /* directory on which mounted */
! long f_syncreads; /* count of sync reads since mount */
! long f_asyncreads; /* count of async reads since mount */
short f_spares1; /* unused spare */
char f_mntfromname[MNAMELEN];/* mounted filesystem */
short f_spares2; /* unused spare */
! long f_spare[2]; /* unused spare */
};
--- 80,98 ----
int f_type; /* type of filesystem */
int f_flags; /* copy of mount exported flags */
! long f_syncwrites; /* count of sync writes since mount */
! long f_asyncwrites; /* count of async writes since mount */
char f_fstypename[MFSNAMELEN]; /* fs type name */
char f_mntonname[MNAMELEN]; /* directory on which mounted */
! long f_syncreads; /* count of sync reads since mount */
! long f_asyncreads; /* count of async reads since mount */
short f_spares1; /* unused spare */
char f_mntfromname[MNAMELEN];/* mounted filesystem */
short f_spares2; /* unused spare */
! /*
! * XXX on machines where longs are aligned to 8-byte boundaries, there
! * is an unnamed int32_t here. This spare was after the apparent end
! * of the struct until we bit off the read counters from f_mntonname.
! */
! long f_spare[2]; /* unused spare */
};
---
I.e., spell `sizeof(long)' correctly and let the compiler calculate the
magic numbers. This still depends on the magic that MNAMELEN is not too
small after biting off a couple of longs from it.
The corresponding fix in user.h would be to write the magic size as the
sum of the sizeof()'s of all the fields, but this would be very fragile
because there would be alignment and padding issues for all the fields.
Padding would have to be explicit.
Bruce
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