fix biosize option

iosizelog shouldn't be the same as iosize but the logarithm of it. Then again the current biosize option doesn't make much sense to me as it doesn't set the preferred I/O size as mentioned in the comment next to it but rather the allocation size and thus is identical to the allocsize option (except for the missing logarithm). It's also not documented in Documentation/filesystems/xfs.txt or the mount manpage.

Signed-off-by Christoph Hellwig <[email protected]>

Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_super.c
===================================================================

ping?

Quoted 10 lines · Christoph Hellwig

iosizelog shouldn't be the same as iosize but the logarithm of it. Then again the current biosize option doesn't make much sense to me as it doesn't set the preferred I/O size as mentioned in the comment next to it but rather the allocation size and thus is identical to the allocsize option (except for the missing logarithm). It's also not documented in Documentation/filesystems/xfs.txt or the mount manpage.

Signed-off-by Christoph Hellwig <[email protected]>

fs/xfs/linux-2.6/xfs_super.c xfs_parseargs( · line 258

Quoted 13 lines

Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_super.c
===================================================================

fs/xfs/linux-2.6/xfs_super.c +1 -1

@@ -252,7 +252,7 @@ xfs_parseargs(
 				return EINVAL;
 			}
 			iosize = simple_strtoul(value, &eov, 10);
-			iosizelog = (uint8_t) iosize;
+			iosizelog = ffs(iosize) - 1;
 		} else if (!strcmp(this_char, MNTOPT_ALLOCSIZE)) {
 			if (!value || !*value) {
 				cmn_err(CE_WARN,

---end quoted text---

iosizelog shouldn't be the same as iosize but the logarithm of it. Then again the current biosize option doesn't make much sense to me as it doesn't set the preferred I/O size as mentioned in the comment next to

it but rather the allocation size and thus is identical to the allocsize option (except for the missing logarithm). It's also not documented in Documentation/filesystems/xfs.txt or the mount manpage.

Quoted 3 lines · Christoph Hellwig

iosizelog shouldn't be the same as iosize but the logarithm of it. Then again the current biosize option doesn't make much sense to me as it doesn't set the preferred I/O size as mentioned in the comment next to

That's a hold-over from irix - biosize set the basic chunk size the cache used for mapping writes, so was effectively the size of write to use to avoid RMW cycles as well as the unit of delayed allocation.

Quoted 3 lines

it but rather the allocation size and thus is identical to the allocsize option (except for the missing logarithm). It's also not documented in Documentation/filesystems/xfs.txt or the mount manpage.

So when it was first added (probably for compatibility) the allocation part was noticed and not the rest. Maybe we should hook it up to xfs_preferred_iosize() rather than allocation now that it exists...