From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Fri, 11 Mar 2011 04:58:10 +0000 (-0800)
Subject: Tweaks to code that handles read-modify-write on data blocks
X-Git-Url: https://git.vrable.net/?a=commitdiff_plain;h=11daa4a2d17850ff5ceb1c30d463d699635cfbc6;p=bluesky.git

Tweaks to code that handles read-modify-write on data blocks
---

diff --git a/bluesky/file.c b/bluesky/file.c
index f10814a..e0c6255 100644
--- a/bluesky/file.c
+++ b/bluesky/file.c
@@ -77,6 +77,15 @@ void bluesky_file_truncate(BlueSkyInode *inode, uint64_t size)
 
     uint64_t blocks = (size + BLUESKY_BLOCK_SIZE - 1) / BLUESKY_BLOCK_SIZE;
 
+    /* Calculate number of bytes in the last block of the file */
+    int lastblock_old, lastblock_new;
+    lastblock_old = inode->size % BLUESKY_BLOCK_SIZE;
+    if (lastblock_old == 0 && inode->size > 0)
+        lastblock_old = BLUESKY_BLOCK_SIZE;
+    lastblock_new = size % BLUESKY_BLOCK_SIZE;
+    if (lastblock_new == 0 && size > 0)
+        lastblock_new = BLUESKY_BLOCK_SIZE;
+
     if (blocks > inode->blocks->len) {
         /* Need to add new blocks to the end of a file.  New block structures
          * are automatically zeroed, which initializes them to be pointers to
@@ -88,10 +97,10 @@ void bluesky_file_truncate(BlueSkyInode *inode, uint64_t size)
                                              inode->blocks->len - 1);
 
             if (b->type != BLUESKY_BLOCK_ZERO
-                    && (b->type == BLUESKY_BLOCK_REF
-                        || b->dirty->len < BLUESKY_BLOCK_SIZE)) {
+                    && lastblock_old < BLUESKY_BLOCK_SIZE) {
                 bluesky_block_touch(inode, inode->blocks->len - 1, TRUE);
                 gsize old_size = b->dirty->len;
+                g_warn_if_fail(lastblock_old != old_size);
                 bluesky_string_resize(b->dirty, BLUESKY_BLOCK_SIZE);
                 memset(&b->dirty->data[old_size], 0,
                        BLUESKY_BLOCK_SIZE - old_size);
@@ -117,7 +126,13 @@ void bluesky_file_truncate(BlueSkyInode *inode, uint64_t size)
         BlueSkyBlock *b = &g_array_index(inode->blocks, BlueSkyBlock,
                                          blocks - 1);
 
-        if (b->type != BLUESKY_BLOCK_ZERO) {
+        gboolean need_resize = TRUE;
+        if (b->type == BLUESKY_BLOCK_ZERO)
+            need_resize = FALSE;
+        else if (size < inode->size && lastblock_new == BLUESKY_BLOCK_SIZE)
+            need_resize = FALSE;
+
+        if (need_resize) {
             bluesky_block_touch(inode, blocks - 1, TRUE);
             gsize old_size = b->dirty->len;
             gsize new_size = size - (blocks - 1) * BLUESKY_BLOCK_SIZE;