clean ufs_trunc_direct() up a bit...

For short files (== no indirect blocks needed) UFS allows the last
block to be a partial one.  That creates some complications for
truncation down to "short file" lengths.  ufs_trunc_direct() is
called when we'd already made sure that new EOF is not in a hole;
nothing needs to be done if we are extending the file and in
case we are shrinking the file it needs to
	* shrink or free the old final block.
	* free all full direct blocks between the new and old EOF.
	* possibly shrink the new final block.

The logics is needlessly complicated by trying to keep all cases
handled by the same sequence of operations.
	if not shrinking
		nothing to do
	else if number of full blocks unchanged
		free the tail of possibly partial last block
	else
		free the tail of (currently full) new last block
		free all present (full) blocks in between
		free the (possibly partial) old last block

is easier to follow than the result of trying to unify these
cases.

Signed-off-by: Al Viro <[email protected]>

Author: Al Viro

fs/ufs/inode.c

@@ -878,91 +878,84 @@ static inline void free_data(struct to_free *ctx, u64 from, unsigned count)
 
 #define DIRECT_FRAGMENT ((inode->i_size + uspi->s_fsize - 1) >> uspi->s_fshift)
 
+/*
+ * used only for truncation down to direct blocks.
+ */
 static void ufs_trunc_direct(struct inode *inode)
 {
 	struct ufs_inode_info *ufsi = UFS_I(inode);
-	struct super_block * sb;
-	struct ufs_sb_private_info * uspi;
-	void *p;
-	u64 frag1, frag2, frag3, frag4, block1, block2;
+	struct super_block *sb = inode->i_sb;
+	struct ufs_sb_private_info *uspi = UFS_SB(sb)->s_uspi;
+	unsigned int new_frags, old_frags;
+	unsigned int old_slot, new_slot;
+	unsigned int old_tail, new_tail;
 	struct to_free ctx = {.inode = inode};
-	unsigned i, tmp;
 
 	UFSD("ENTER: ino %lu\n", inode->i_ino);
 
-	sb = inode->i_sb;
-	uspi = UFS_SB(sb)->s_uspi;
-
-	frag1 = DIRECT_FRAGMENT;
-	frag4 = min_t(u64, UFS_NDIR_FRAGMENT, ufsi->i_lastfrag);
-	frag2 = ((frag1 & uspi->s_fpbmask) ? ((frag1 | uspi->s_fpbmask) + 1) : frag1);
-	frag3 = frag4 & ~uspi->s_fpbmask;
-	block1 = block2 = 0;
-	if (frag2 > frag3) {
-		frag2 = frag4;
-		frag3 = frag4 = 0;
-	} else if (frag2 < frag3) {
-		block1 = ufs_fragstoblks (frag2);
-		block2 = ufs_fragstoblks (frag3);
-	}
-
-	UFSD("ino %lu, frag1 %llu, frag2 %llu, block1 %llu, block2 %llu,"
-	     " frag3 %llu, frag4 %llu\n", inode->i_ino,
-	     (unsigned long long)frag1, (unsigned long long)frag2,
-	     (unsigned long long)block1, (unsigned long long)block2,
-	     (unsigned long long)frag3, (unsigned long long)frag4);
+	new_frags = DIRECT_FRAGMENT;
+	// new_frags = first fragment past the new EOF
+	old_frags = min_t(u64, UFS_NDIR_FRAGMENT, ufsi->i_lastfrag);
+	// old_frags = first fragment past the old EOF or covered by indirects
 
-	if (frag1 >= frag2)
-		goto next1;
-
-	/*
-	 * Free first free fragments
-	 */
-	p = ufs_get_direct_data_ptr(uspi, ufsi, ufs_fragstoblks(frag1));
-	tmp = ufs_data_ptr_to_cpu(sb, p);
-	if (!tmp )
-		ufs_panic (sb, "ufs_trunc_direct", "internal error");
-	frag2 -= frag1;
-	frag1 = ufs_fragnum (frag1);
+	if (new_frags >= old_frags)	 // expanding - nothing to free
+		goto done;
 
-	ufs_free_fragments(inode, tmp + frag1, frag2);
+	old_tail = ufs_fragnum(old_frags);
+	old_slot = ufs_fragstoblks(old_frags);
+	new_tail = ufs_fragnum(new_frags);
+	new_slot = ufs_fragstoblks(new_frags);
 
-next1:
-	/*
-	 * Free whole blocks
-	 */
-	for (i = block1 ; i < block2; i++) {
-		p = ufs_get_direct_data_ptr(uspi, ufsi, i);
-		tmp = ufs_data_ptr_to_cpu(sb, p);
+	if (old_slot == new_slot) { // old_tail > 0
+		void *p = ufs_get_direct_data_ptr(uspi, ufsi, old_slot);
+		u64 tmp = ufs_data_ptr_to_cpu(sb, p);
 		if (!tmp)
-			continue;
-		write_seqlock(&ufsi->meta_lock);
-		ufs_data_ptr_clear(uspi, p);
-		write_sequnlock(&ufsi->meta_lock);
+			ufs_panic(sb, __func__, "internal error");
+		if (!new_tail) {
+			write_seqlock(&ufsi->meta_lock);
+			ufs_data_ptr_clear(uspi, p);
+			write_sequnlock(&ufsi->meta_lock);
+		}
+		ufs_free_fragments(inode, tmp + new_tail, old_tail - new_tail);
+	} else {
+		unsigned int slot = new_slot;
 
-		free_data(&ctx, tmp, uspi->s_fpb);
-	}
+		if (new_tail) {
+			void *p = ufs_get_direct_data_ptr(uspi, ufsi, slot++);
+			u64 tmp = ufs_data_ptr_to_cpu(sb, p);
+			if (!tmp)
+				ufs_panic(sb, __func__, "internal error");
 
-	free_data(&ctx, 0, 0);
+			ufs_free_fragments(inode, tmp + new_tail,
+						uspi->s_fpb - new_tail);
+		}
+		while (slot < old_slot) {
+			void *p = ufs_get_direct_data_ptr(uspi, ufsi, slot++);
+			u64 tmp = ufs_data_ptr_to_cpu(sb, p);
+			if (!tmp)
+				continue;
+			write_seqlock(&ufsi->meta_lock);
+			ufs_data_ptr_clear(uspi, p);
+			write_sequnlock(&ufsi->meta_lock);
 
-	if (frag3 >= frag4)
-		goto next3;
+			free_data(&ctx, tmp, uspi->s_fpb);
+		}
 
-	/*
-	 * Free last free fragments
-	 */
-	p = ufs_get_direct_data_ptr(uspi, ufsi, ufs_fragstoblks(frag3));
-	tmp = ufs_data_ptr_to_cpu(sb, p);
-	if (!tmp )
-		ufs_panic(sb, "ufs_truncate_direct", "internal error");
-	frag4 = ufs_fragnum (frag4);
-	write_seqlock(&ufsi->meta_lock);
-	ufs_data_ptr_clear(uspi, p);
-	write_sequnlock(&ufsi->meta_lock);
+		free_data(&ctx, 0, 0);
 
-	ufs_free_fragments (inode, tmp, frag4);
- next3:
+		if (old_tail) {
+			void *p = ufs_get_direct_data_ptr(uspi, ufsi, slot);
+			u64 tmp = ufs_data_ptr_to_cpu(sb, p);
+			if (!tmp)
+				ufs_panic(sb, __func__, "internal error");
+			write_seqlock(&ufsi->meta_lock);
+			ufs_data_ptr_clear(uspi, p);
+			write_sequnlock(&ufsi->meta_lock);
 
+			ufs_free_fragments(inode, tmp, old_tail);
+		}
+	}
+done:
 	UFSD("EXIT: ino %lu\n", inode->i_ino);
 }