rework of overlay, region={beg,end}

diff --git a/fusefile.c b/fusefile.c
index 30ec7fa284c7ce1f330daaede1de2fb1835ee9b5..01f4c58400f0d4a2197797ddebb6a415e27b808a 100644 (file)
--- a/fusefile.c
+++ b/fusefile.c
@@ -35,8 +35,8 @@
 #include <errno.h>
 
 struct Region {
-    off_t pos;
-    size_t size;
+    off_t beg;
+    off_t end;
 };
 
 struct Source {
@@ -72,18 +72,18 @@ static struct {
 
 static void usage();
 
-#define FRAG(m) (overlay.table+m)
-#define BEG(m) (FRAG(m)->pos)
-#define END(m) (FRAG(m)->pos + FRAG(m)->size)
-
+/**
+ * Find the nearest overlay.table region below pos. Returns the index,
+ * or -1 if there is none, i.e. pos < overlay.table[0].
+ */
 static ssize_t overlay_prior_fragment(off_t pos) {
     size_t lo = 0, hi = overlay.count;
     while ( lo < hi ) {
        size_t m = ( lo + hi ) / 2;
        if ( m == lo ) {
-           return BEG( m ) < pos? m : -1;
+           return overlay.table[m].beg <= pos? m : -1;
        }
-       if ( BEG( m ) <= pos ) {
+       if ( overlay.table[m].beg <= pos ) {
            lo = m;
        } else {
            hi = m;
@@ -92,6 +92,11 @@ static ssize_t overlay_prior_fragment(off_t pos) {
     return -1;
 }
 
+/**
+ * Save the entry count for overlay.table as 64-bit integer
+ * immediately following the overlay content at the index
+ * corresponding to the fused file size.
+ */
 static void overlay_save_count() {
     lseek( overlay.source.fd, overlay.source.to, SEEK_SET );
     size_t size = sizeof( overlay.count );
@@ -111,8 +116,13 @@ static void overlay_save_count() {
     }
 }
 
+/**
+ * Update the on-disk cache of overlay.table between the given
+ * indexes. The table is laid out immediately following the table
+ * count with each region saved as two 64-bit unsigned integers.
+ */
 static void overlay_save_table(size_t lo,size_t hi) {
-    char *p = (char *) FRAG(lo);
+    char *p = (char *) &overlay.table[ lo ];
     size_t pos =  overlay.source.to + sizeof( overlay.count ) +
        lo * sizeof( struct Region );
     size_t size = ( hi - lo ) * sizeof( struct Region );
@@ -135,8 +145,13 @@ static void overlay_save_table(size_t lo,size_t hi) {
     }
 }
 
-static void overlay_insert(size_t p,off_t pos,size_t size) {
+/**
+ * Insert a new region at index p, with previous portion [p,count]
+ * moved up to make space.
+ */
+static void overlay_insert(size_t p,off_t beg,off_t end) {
     size_t bytes;
+    // Grow the table if needed
     if ( overlay.count >= overlay.limit ) {
        overlay.limit = overlay.count + 10;
        bytes = overlay.limit * sizeof( struct Region );
@@ -145,84 +160,111 @@ static void overlay_insert(size_t p,off_t pos,size_t size) {
     }
     bytes = ( overlay.count++ - p ) * sizeof( struct Region );
     if ( bytes ) {
-       memmove( FRAG( p+1 ), FRAG( p ), bytes );
+       memmove( (char*) &overlay.table[ p+1 ],
+                (char*) &overlay.table[ p ],
+                bytes );
     }
-    FRAG( p )->pos = pos;
-    FRAG( p )->size = size;
+    overlay.table[ p ].beg = beg;
+    overlay.table[ p ].end = end;
     overlay_save_count();
 }
 
+/**
+ * Delete the region entry at p by moving the portion [p+1,count]
+ * down.
+ */
 static void overlay_delete(size_t p) {
-    if ( p < --overlay.count ) {
-       size_t size = ( overlay.count - p ) * sizeof( struct Region );
-       memmove( FRAG(p), FRAG(p+1), size );
+    size_t bytes = ( --overlay.count - p ) * sizeof( struct Region );
+    if ( bytes ) {
+       memmove( (char*) &overlay.table[ p ],
+                (char*) &overlay.table[ p+1 ],
+                bytes );
     }
-    overlay_save_count();
 }
 
-static void overlay_mark(off_t pos,size_t size) {
+/**
+ * Mark the given region as updated, i.e. written to the overlay. The
+ * mark region may attach to prior marked regions ro be a new,
+ * separate region. If attaching, it causes the prior regions to
+ * expand and the table adjusted by deleting any regions that become
+ * fully contained in other regions.
+ */
+static void overlay_mark(off_t beg,off_t end) {
 #if DEBUG
-    fprintf( stderr, "overlay_mark( %ld, %ld )\n", pos, size );
+    fprintf( stderr, "overlay_mark( %ld, %ld )\n", beg, end );
 #endif
     int deleted = 0;
     ssize_t q;
-    ssize_t p = overlay_prior_fragment( pos );
-    // p is the nearest region below pos (or -1)
-    if ( p >= 0 && pos <= END(p) ) {
+    ssize_t p = overlay_prior_fragment( beg );
+    // p is the nearest region below or at beg (or -1)
+    if ( p >= 0 && beg <= overlay.table[p].end ) {
        // p overlaps mark region
-       if ( END(p) >= pos + size ) {
+       if ( end <= overlay.table[p].end ) {
+           // region p covers mark region already
 #if DEBUG
-       fprintf( stderr, "overlay size 1( %ld )\n", FRAG(p)->size );
+           fprintf( stderr, "overlay covering ( %ld %ld )\n",
+                    overlay.table[p].beg, overlay.table[p].end );
 #endif
-           return; // new mark within existing.
+           return;
        }
-       // new mark region extends existing
-       FRAG(p)->size = pos + size - BEG(p);
+       // the new mark region extends region p
+       overlay.table[p].end = end;
        q = p+1;
-       while ( q < overlay.count && BEG(q) <= END(p) ) {
-           if ( END(q) > END(p) ) {
-               FRAG(p)->size = END(q) - BEG(p);
+       while ( q < overlay.count &&
+               overlay.table[q].beg <= overlay.table[p].end ) {
+           // Extended region merges with subsequent region
+           if ( overlay.table[p].end < overlay.table[q].end ) {
+               overlay.table[p].end = overlay.table[q].end;
            }
            overlay_delete( q );
            deleted++;
        }
-       overlay_save_table( p, deleted? overlay.count : q );
+       if ( deleted ) {
+           overlay_save_count();
+           q = overlay.count;
+       }
+       overlay_save_table( p, q );
 #if DEBUG
-       fprintf( stderr, "overlay size 2( %ld ) deleted %d\n",
-                FRAG(p)->size, deleted );
+       fprintf( stderr, "overlay expand ( %ld %ld ) deleted %d\n",
+                overlay.table[p].beg, overlay.table[p].end, deleted );
 #endif
        return;
     }
-    // The region p does not expand into new mark region
-    p++; // subsequent region
-    if ( p >= overlay.count || BEG(p) > pos + size ) {
-       // New mark is separate region at p
-       overlay_insert( p, pos, size);
+    // The prior region p does not expand into new mark region
+    p++; // subsequent region 
+    if ( p >= overlay.count || end < overlay.table[p].beg ) {
+       // New mark region is a separate region at p
+       overlay_insert( p, beg, end );
 #if DEBUG
-       fprintf( stderr, "overlay size 4( %ld )\n", FRAG(p)->size );
+       fprintf( stderr, "overlay new ( %ld %ld )\n",
+                overlay.table[p].beg, overlay.table[p].end );
 #endif
        overlay_save_table( p, overlay.count );
        return;
     }
-    // New marks start before and overlap with the region
-    if ( BEG(p) + FRAG(p)->size < pos + size ) {
-       FRAG(p)->size = size; // new mark covers old region
-    } else {
-       FRAG(p)->size += BEG(p) - pos;
-    }
-    BEG(p) = pos;
+    // New marks start before and overlap with region p => change p
+    // and handle any subsequent regions being covered
+    overlay.table[p].beg = beg;
     q = p+1;
-    while ( q < overlay.count && BEG(q) <= END(p) ) {
-       if ( END(q) > END(p) ) {
-           FRAG(p)->size = END(q) - BEG(p);
+    if ( overlay.table[p].end < end ) {
+       overlay.table[p].end = end;
+       while ( q < overlay.count &&
+               overlay.table[q].beg <= overlay.table[p].end ) {
+           if ( overlay.table[p].end < overlay.table[q].end ) {
+               overlay.table[p].end = overlay.table[q].end;
+           }
+           overlay_delete( q );
+           deleted++;
+       }
+       if ( deleted ) {
+           overlay_save_count();
+           q = overlay.count;
        }
-       overlay_delete( q );
-       deleted++;
     }
-    overlay_save_table( p, deleted? overlay.count : q );
+    overlay_save_table( p, q );
 #if DEBUG
-    fprintf( stderr, "overlay size 4( %ld ) deleted %d\n",
-            FRAG(p)->size, deleted );
+    fprintf( stderr, "overlay before ( %ld %ld ) deleted %d\n",
+            overlay.table[p].beg, overlay.table[p].end, deleted );
 #endif
 }
 
@@ -406,43 +448,34 @@ static int find_source(off_t offset) {
     return lo;
 }
 
-static int overlay_merge(char *buf,off_t off,size_t size) {
+static int overlay_merge(char *buf,off_t beg,off_t end) {
 #if DEBUG
-    fprintf( stderr, "merge %ld %ld\n", off, size );
+    fprintf( stderr, "merge %ld %ld\n", beg, end );
 #endif
-    // Find nearest overlay data before or at off
-    ssize_t p = overlay_prior_fragment( off );
+    // Find nearest overlay data before or at beg
+    ssize_t p = overlay_prior_fragment( beg );
     if ( p < 0 ) {
        p = 0;
     }
-    for ( ; p < overlay.count && BEG(p) < off+size; p++ ) {
-       if ( END(p) < off ) {
+    for ( ; p < overlay.count && overlay.table[p].beg < end; p++ ) {
+       if ( overlay.table[p].end < beg ) {
            continue;
        }
-       size_t delta = FRAG(p)->size;
-       if ( BEG(p) < off ) {
-           delta -= off - BEG(p);
-       } else {
-           size_t skip = BEG(p) - off;
-           off += skip;
-           size -= skip;
-           buf += skip;
-       }
-       if ( delta > size ) {
-           delta = size;
+       if ( overlay.table[p].beg > beg ) {
+           size_t delta = overlay.table[p].beg - beg;
+           buf += delta;
+           beg += delta;
        }
-       lseek( overlay.source.fd, off, SEEK_SET );
-       while ( delta > 0 ) {
-           size_t n = read( overlay.source.fd, buf, delta );
-           off += n;
+       size_t size = ( overlay.table[p].end <= end )?
+           ( overlay.table[p].end - beg ) : ( end - beg ); 
+       lseek( overlay.source.fd, beg, SEEK_SET );
+       while ( size > 0 ) {
+           size_t n = read( overlay.source.fd, buf, size );
            size -= n;
-           delta -= n;
            buf += n;
+           beg += n; //
        }
     }
-#if DEBUG
-    fprintf( stderr, "merged\n" );
-#endif
     return 0;
 }
 
@@ -511,7 +544,7 @@ static int fusefile_read(const char *path, char *buf, size_t size,
                fsync( overlay.source.fd );
                overlay.source.dirty = 0;
            }
-           int x = overlay_merge( buf + rr, off + rr, r );
+           int x = overlay_merge( buf + rr, off + rr, off + rr + r );
            if ( x ) {
                return x;
            }
@@ -563,9 +596,9 @@ static void overlay_load() {
            exit( 1 );
        }
 #if DEBUG
-       fprintf( stderr, "overlay region: %ld %ld\n", f.pos, f.size );
+       fprintf( stderr, "overlay region: %ld %ld\n", f.beg, f.end );
 #endif
-       overlay_mark( f.pos, f.size );
+       overlay_mark( f.beg, f.end );
     }
 }
 
@@ -577,7 +610,7 @@ static int write_block(off_t off,const char *buf,size_t size) {
     fprintf( stderr, "write_block( %ld, ?, %ld )\n", off, size );
 #endif
     if ( overlay.source.filename ) {
-       overlay_mark( off, size ); // Mark region as written
+       overlay_mark( off, off + size ); // Mark region as written
     }
     while ( size > 0 ) {
        int index = find_source( off ); // index of source file