On May 05, 2009 14:25 -0600, Andreas Dilger wrote: > we're looking to store some extended data in each directory entry > for Lustre, to hold a 128-bit filesystem-unique file identifier > in the dirent. If we ever wanted to look at 64-bit or larger > inode numbers we would need to do the same. > > In order to detect the presence of this extra data in the dirent, we > would want to use the high bits in d_type (say bits 0xf0). This part > of d_type could be a flag for the presence of 4 different types of > data (which limits the number of different kinds of data). The d_type > would mask off the high bits in get_dtype() so as not to confuse filldir. Ted, could we at least reserve the INCOMPAT_DIRDATA flag to avoid conflicts: #define EXT4_FEATURE_INCOMPAT_DIRDATA 0x1000 reserve the high 4 bits of d_type: #define EXT4_DIRENT_LUFID 0x10 /* Lustre 128-bit unique file identifier */ 0x20, 0x40, and 0x80 would be available for future expansion (e.g. high 32 bits of inode number). If needed, type 0x80 can be extended by adding a 1-byte subtype after the length byte, though I doubt this would be needed. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
