On Nov 23, 2008 00:48 +0600, Alexey Salmin wrote:
> Sure, I understand the problems you've mentioned. But every big act
> has the beginning. Adding the extension to the ext4 is only the first
> step. Of course it'll cause crashes and other problems in many places
> from kernel to userspace code. But these problems will disturb only
> people who will really use this extension (like me). Anyway most of these
> bugs will be fixed some day, may be in two or three years. No one is
> talking that it's a fast process but it will reach it's end and that's good
> I think.
If you are motivated to work on this, there are a number of possible ways
that this could be done. The simplest would be to create a new directory
entry (replacing ext4_dir_entry_2) that has a longer name_len field, and
ideally it would also have space for a 48-bit inode number (ext4 will
NEVER need more than 280 trillion inodes I think).
I don't know that it is practical to require this format for the entire
directory, because it would mean in some rare cases rewriting 1M entries
(or whatever) in a large directory to the new format. It would be better
to allow either just the leaf block to hold the new record format (with a
marker at the start of the block), or individual records having the new
format, possibly marked by a bit in the "file_type" field.
It's kind of ugly, but it needs to be possible to detect if the entry is
the old format or the new one.
#define EXT4_DIRENT3_FL 0x00400000 /* directory has any dir_entry_3 */
#define EXT4_FT_ENTRY_3 0x80 /* file_type for dir_entry_3 */
#define EXT4_FT_MASK 0x0f /* EXT4_FT_* mask */
#define EXT4_INODE_MASK 0x00ffffffffffffff /* 48-bit inode number mask */
#define EXT4_NAME_LEN3 1012
struct ext4_dir_entry_3 {
__le64 inode; /* High byte holds file_type */
__le16 rec_len;
__le16 name_len;
char name[EXT4_NAME_LEN3];
};
static inline __u8 ext4_get_de_file_type(struct ext4_dir_entry_2 *dirent)
{
return (dirent->file_type & EXT4_FT_MASK);
}
static inline int ext4_get_de_name_len(struct ext4_dir_entry_2 *dirent)
{
if (dirent->file_type & EXT4_FT_ENTRY_3) {
struct ext4_dir_entry_3 *dirent3 = dirent;
return le16_to_cpu(dirent3->name_len);
}
return dirent->name_len;
}
static inline int ext4_get_de_rec_len(struct ext4_dir_entry_2 *dirent)
{
if (dirent->file_type & EXT4_FT_ENTRY_3) {
struct ext4_dir_entry_3 *dirent3 = dirent;
return le16_to_cpu(dirent3->rec_len);
}
return le16_to_cpu(dirent->rec_len);
}
static inline __u64 ext4_get_de_inode(struct ext4_dir_entry_2 *dirent)
{
if (dirent->file_type & EXT4_FT_ENTRY_3) {
struct ext4_dir_entry_3 *dirent3 = dirent;
return le64_to_cpu(dirent3->inode) & EXT4_INODE_MASK;
}
return le32_to_cpu(dirent->inode);
}
static inline __u64 ext4_get_de_name(struct ext4_dir_entry_2 *dirent)
{
if (dirent->file_type & EXT4_FT_ENTRY_3) {
struct ext4_dir_entry_3 *dirent3 = dirent;
return dirent3->name;
}
return dirent->name);
}
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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