Re: [reiserfs-dev] Re: [PATCH] sparc32: wrong type of nlink_t

[Tomas Szepe]

> >>>  Against 2.4.20-pre5 - fix up the type of nlink_t. This makes jfs and
> >>>  reiserfs stop complaining about comparisons always turning up false
> >>>  due to limited range of data type.
> >>>
> >>>If you change this, you change the types exported to userspace
> >>>which will break everything.
> >>>     
> >>>
> >>Right.  Here's a corresponding reiserfs/jfs fix, then.  I've checked the
> >>constants aren't used for anything else except nlink overflow alerts.
> >>   
> >>
> >
> >I don't like this fix.  I know 32767 is a lot of links, but I don't like
> >artificially lowering a limit like this just because one architecture
> >defines nlink_t incorrectly.  I'd rather get rid of the compiler warnings
> >with a cast in the few places the limit is checked, even though that is
> >a little bit ugly.
> >
> > 
> >
> >>diff -urN linux-2.4.20-pre5/fs/jfs/jfs_filsys.h 
> >>linux-2.4.20-pre5.n/fs/jfs/jfs_filsys.h
> >>--- linux-2.4.20-pre5/fs/jfs/jfs_filsys.h	2002-09-01 
> >>11:31:44.000000000 +0200
> >>+++ linux-2.4.20-pre5.n/fs/jfs/jfs_filsys.h	2002-09-01 
> >>11:30:13.000000000 +0200
> >>@@ -125,7 +125,8 @@
> >>#define MAXBLOCKSIZE		4096
> >>#define	MAXFILESIZE		((s64)1 << 52)
> >>
> >>-#define JFS_LINK_MAX		65535	/* nlink_t is unsigned short 
> >>*/
> >>+/* the shortest nlink_t there is is sparc's signed short */
> >>+#define JFS_LINK_MAX		32767
> >>
> >>/* Minimum number of bytes supported for a JFS partition */
> >>#define MINJFS			(0x1000000)
> >>diff -urN linux-2.4.20-pre5/include/linux/reiserfs_fs.h 
> >>linux-2.4.20-pre5.n/include/linux/reiserfs_fs.h
> >>--- linux-2.4.20-pre5/include/linux/reiserfs_fs.h	2002-09-01 
> >>11:31:45.000000000 +0200
> >>+++ linux-2.4.20-pre5.n/include/linux/reiserfs_fs.h	2002-09-01 
> >>11:23:30.000000000 +0200
> >>@@ -1185,10 +1185,12 @@
> >>#define MAX_B_NUM  MAX_UL_INT
> >>#define MAX_FC_NUM MAX_US_INT
> >>
> >>-
> >>-/* the purpose is to detect overflow of an unsigned short */
> >>-#define REISERFS_LINK_MAX (MAX_US_INT - 1000)
> >>-
> >>+/* the original purpose was to detect a possible overflow
> >>+ * of an unsigned short nlink_t. However, there are archs
> >>+ * that only provide a signed short nlink_t, so this will
> >>+ * have to start ringing a wee bit earlier.
> >>+ */
> >>+#define REISERFS_LINK_MAX (0x7fff - 1000)
> >>
> >>/* The following defines are used in reiserfs_insert_item and 
> >>reiserfs_append_item  */
> >>#define REISERFS_KERNEL_MEM		0	/* reiserfs kernel memory 
> >>mode	*/
> >>   
> >>
> >
> >Thanks,
> >Shaggy
> >
> > 
> >
> I think you are sort of right.  You are right to dislike this patch for 
> the reasons you state.  The proper fix should be to make the result of 
> the limit computation be accurately architecture specific.   I wasn't 
> paying enough attention --- hardcoding
> 
> 0x7fff - 1000 
> 
> is ugly.  We need to find some appropriate #define to subtract 1000 from.
> 
> Green, please scan the code for the magic constant to compute from, and 
> code something unless Dave or someone does it before you.

All right, how about this? ->

typedef unsigned long long u64;

/* usable for char, short int, and int */
#define set_to_max(a) \
{ \
	u64 max = ((u64) 2 << (sizeof(a) * 8 - 1)) - 1; \
	a = max; if ((u64) a != max) a = max / 2; \
}

Tomas