Remove struct lfs_direct (no longer used) and update the big block
comment about directories.
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dholland
parent
805a8504cb
commit
7ad6b1a922
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@ -1,4 +1,4 @@
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/* $NetBSD: lfs.h,v 1.188 2015/09/15 15:02:01 dholland Exp $ */
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/* $NetBSD: lfs.h,v 1.189 2015/09/15 15:02:40 dholland Exp $ */
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/* from NetBSD: dinode.h,v 1.22 2013/01/22 09:39:18 dholland Exp */
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/* from NetBSD: dir.h,v 1.21 2009/07/22 04:49:19 dholland Exp */
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@ -228,15 +228,15 @@
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* All strings include a null terminator; the maximum string length
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* is LFS_MAXNAMLEN, which is 255.
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*
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* The directory entry structure (struct lfs_direct) includes both the
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* header and a maximal string. A real entry is potentially smaller;
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* this causes assorted complications and hazards. For example, if
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* pointing at the last entry in a directory block, in most cases the
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* end of the struct lfs_direct will be off the end of the block
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* buffer and pointing into some other memory (or into the void); thus
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* one must never e.g. assign structures directly or do anything that
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* accesses the name field beyond the real length stored in the
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* header.
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* The directory entry header structure (struct lfs_dirheader) is just
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* the header information. A complete entry is this plus a null-
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* terminated name following it, plus some amount of padding. The
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* length of the name (not including the null terminator) is given by
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* the namlen field of the header; the complete record length,
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* including the null terminator and padding, is given by the reclen
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* field of the header. The record length is always 4-byte aligned.
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* (Even on 64-bit volumes, the record length is only 4-byte aligned,
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* not 8-byte.)
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*
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* Historically, FFS directories were/are organized into blocks of
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* size DIRBLKSIZE that can be written atomically to disk at the
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@ -263,6 +263,8 @@
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* - any particular entry may be arbitrarily larger (which is why the
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* header stores both the entry size and the name size) to pad out
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* unused space.
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* - historically the padding in an entry is not necessarily zeroed
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* but may contain trash.
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* - dp->d_reclen is the size of the entry. This is always 4-byte
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* aligned.
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* - dp->d_namlen is the length of the string, and should always be
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@ -276,56 +278,37 @@
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* removed their space is merged into the entry ahead of them.
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* - an empty/unused entry has d_ino set to 0. This normally only
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* appears in the first entry in a block, as elsewhere the unused
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* entry should have been merged into the one before it.
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* entry should have been merged into the one before it. However,
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* fsck leaves such entries behind so they must be tolerated
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* elsewhere.
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* - a completely empty directory block has one entry whose
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* d_reclen is DIRBLKSIZ and whose d_ino is 0.
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*
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* LFS_OLDDIRFMT and LFS_NEWDIRFMT are code numbers for a directory
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* format change that happened in ffs a long time ago. This was in the
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* 80s, if I'm not mistaken, and well before LFS was first written, so
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* there should be no LFS volumes (and certainly no LFS v2-format
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* volumes, or LFS64 volumes) where LFS_OLDDIRFMT pertains. All the
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* same, we get to carry the logic around until we can conclusively
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* demonstrate that it's never needed.
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* The "old directory format" referenced by the fs->lfs_isolddirfmt
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* flag (and some other things) refers to when the type field was
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* added to directory entries. This change was made to FFS in the 80s,
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* well before LFS was first written; there should be no LFS volumes
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* (and certainly no LFS v2-format volumes or LFS64 volumes) where the
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* old format pertains. All of the related logic should probably be
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* removed; however, it hasn't been yet, and we get to carry it around
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* until we can be conclusively sure it isn't needed.
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*
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* Note that these code numbers do not appear on disk. They're
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* generated from runtime logic that is cued by other things, which is
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* why LFS_OLDDIRFMT is confusingly 1 and LFS_NEWDIRFMT is confusingly
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* 0.
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* In the "old directory format" there is no type field and the namlen
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* field is correspondingly 16 bits wide. On big-endian volumes this
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* has no effect: namlen cannot exceed 255, so the upper byte is
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* always 0 and this reads back from the type field as LFS_DT_UNKNOWN.
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* On little-endian volumes, the namlen field will always be 0 and
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* the namlen value needs to be read out of the type field. (The type
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* is always LFS_DT_UNKNOWN.) The directory accessor functions take
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* care of this so nothing else needs to be aware of it.
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*
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* Relatedly, the byte swapping logic for directories we have, which
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* is derived from the FFS_EI code, is a horrible mess. For example,
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* to access the namlen field, one does the following:
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* LFS_OLDDIRFMT and LFS_NEWDIRFMT are code numbers for the old and
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* new directory format respectively. These codes do not appear on
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* disk; they're generated from a runtime macro called FSFMT() that's
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* cued by other things. This is why (confusingly) LFS_OLDDIRFMT is 1
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* and LFS_NEWDIRFMT is 0.
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*
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* #if (BYTE_ORDER == LITTLE_ENDIAN)
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* swap = (ULFS_IPNEEDSWAP(VTOI(vp)) == 0);
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* #else
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* swap = (ULFS_IPNEEDSWAP(VTOI(vp)) != 0);
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* #endif
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* return ((FSFMT(vp) && swap)? ep->d_type : ep->d_namlen);
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*
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* ULFS_IPNEEDSWAP() is the same as fetching fs->lfs_dobyteswap. This
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* horrible "swap" logic is cutpasted all over everywhere but amounts
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* to the following:
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*
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* running code volume lfs_dobyteswap "swap"
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* ----------------------------------------------------------
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* LITTLE_ENDIAN LITTLE_ENDIAN false true
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* LITTLE_ENDIAN BIG_ENDIAN true false
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* BIG_ENDIAN LITTLE_ENDIAN true true
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* BIG_ENDIAN BIG_ENDIAN false false
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*
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* which you'll note boils down to "volume is little-endian".
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*
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* Meanwhile, FSFMT(vp) yields LFS_OLDDIRFMT or LFS_NEWDIRFMT via
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* perverted logic of its own. Since LFS_OLDDIRFMT is 1 (contrary to
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* what one might expect approaching this cold) what this mess means
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* is: on OLDDIRFMT volumes that are little-endian, we read the
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* namlen value out of the type field. This is because on OLDDIRFMT
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* volumes there is no d_type field, just a 16-bit d_namlen; so if
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* the 16-bit d_namlen is little-endian, the useful part of it is
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* in the first byte, which in the NEWDIRFMT structure is the d_type
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* field.
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* FSFMT(), LFS_OLDDIRFMT, and LFS_NEWDIRFMT should be removed. (XXX)
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*/
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/*
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@ -371,10 +354,6 @@ struct lfs_dirheader {
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u_int8_t dh_type; /* file type, see below */
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u_int8_t dh_namlen; /* length of string in d_name */
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};
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struct lfs_direct {
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struct lfs_dirheader d_header;
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char d_name[LFS_MAXNAMLEN + 1];/* name with length <= LFS_MAXNAMLEN */
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};
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/*
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* Template for manipulating directories. Should use struct lfs_direct's,
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