X-Git-Url: https://git.rrq.au/?a=blobdiff_plain;f=fusefile.c;h=a1bf2bd926792844ecee3c989dd131da641d69e2;hb=HEAD;hp=59dcaa5fb746b13f90098c69c7e278b21b73490e;hpb=f2a64b0bd6a5624ec37ec31a07747bfb063a7bb6;p=rrq%2Ffusefile.git

diff --git a/fusefile.c b/fusefile.c
index 59dcaa5..a1bf2bd 100644
--- a/fusefile.c
+++ b/fusefile.c
@@ -1,8 +1,8 @@
 /***
     fusefile - overlay a file path with a concatenation of parts of
-    other files, read only.
+    other files.
 
-    Copyright (C) 2019  Ralph Ronnquist
+    Copyright (C) 2019-  Ralph Ronnquist
 
     This program is free software: you can redistribute it and/or
     modify it under the terms of the GNU General Public License as
@@ -33,6 +33,15 @@
 #include <unistd.h>
 #include <time.h>
 #include <errno.h>
+#include <sys/ioctl.h>
+#include <linux/fs.h>
+
+struct Region {
+    off_t beg;
+    off_t end;
+};
+
+#define REGIONKEEP(r) ((r,beg == r.end)?: 0 : 1)
 
 struct Source {
     char *filename;
@@ -40,8 +49,11 @@ struct Source {
     ssize_t to;
     ssize_t start; // starting position in concatenated file
     int fd;
+    int dirty;
 };
 
+#define ENDSOURCE( S ) ( S.start + ( S.to - S.from ) )
+
 static struct {
     struct Source *array;
     int count;
@@ -53,7 +65,236 @@ static struct {
     time_t mtime;
     time_t ctime;
 } times;
-    
+
+/**
+ * Overlay
+ */
+static struct Overlay {
+    struct Source source;
+    struct Region *table;
+    size_t count;
+    size_t limit;
+} overlay; // The current overlay.
+
+static void usage();
+
+/**
+ * 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 overlay.table[m].beg <= pos? m : -1;
+	}
+	if ( overlay.table[m].beg <= pos ) {
+	    lo = m;
+	} else {
+	    hi = m;
+	}
+    }
+    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 );
+    char *p = (char *) &overlay.count ;
+    while ( size > 0 ) {
+	size_t n = write( overlay.source.fd, p, size );
+	if ( n < 0 ) {
+	    perror( overlay.source.filename );
+	    exit( 1 );
+	}
+	size -= n;
+	p += n;
+    }
+    if ( overlay.source.dirty++ > 1000 ) {
+	fsync( overlay.source.fd );
+	overlay.source.dirty = 0;
+    }
+}
+
+/**
+ * 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 *) &overlay.table[ lo ];
+    size_t pos =  overlay.source.to + sizeof( overlay.count ) +
+	lo * sizeof( struct Region );
+    size_t size = ( hi - lo ) * sizeof( struct Region );
+    if ( pos != lseek( overlay.source.fd, pos, SEEK_SET ) ) {
+	fprintf( stderr, "%s: seek error\n", overlay.source.filename );
+	exit( 1 );
+    }
+    while ( size > 0 ) {
+	size_t n = write( overlay.source.fd, p, size );
+	if ( n < 0 ) {
+	    perror( overlay.source.filename );
+	    exit( 1 );
+	}
+	size -= n;
+	p += n;
+    }
+    if ( overlay.source.dirty++ > 1000 ) {
+	fsync( overlay.source.fd );
+	overlay.source.dirty = 0;
+    }
+}
+
+/**
+ * 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 );
+	overlay.table = overlay.table?
+	    realloc( overlay.table, bytes ) : malloc( bytes );
+    }
+    bytes = ( overlay.count++ - p ) * sizeof( struct Region );
+    if ( bytes ) {
+	memmove( (char*) &overlay.table[ p+1 ],
+		 (char*) &overlay.table[ p ],
+		 bytes );
+    }
+    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) {
+    size_t bytes = ( --overlay.count - p ) * sizeof( struct Region );
+    if ( bytes ) {
+	memmove( (char*) &overlay.table[ p ],
+		 (char*) &overlay.table[ p+1 ],
+		 bytes );
+    }
+}
+
+/**
+ * Mark the given region as updated, i.e. written to the overlay. The
+ * mark region may attach to prior marked regions or 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", beg, end );
+#endif
+    int deleted = 0;
+    ssize_t q;
+    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 <= overlay.table[p].end ) {
+	    // region p covers mark region already
+#if DEBUG
+	    fprintf( stderr, "overlay covering ( %ld %ld )\n",
+		     overlay.table[p].beg, overlay.table[p].end );
+#endif
+	    return;
+	}
+	// the new mark region extends region p
+	overlay.table[p].end = end;
+	q = p+1;
+	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++;
+	}
+	if ( deleted ) {
+	    overlay_save_count();
+	    q = overlay.count;
+	}
+	overlay_save_table( p, q );
+#if DEBUG
+	fprintf( stderr, "overlay expand ( %ld %ld ) deleted %d\n",
+		 overlay.table[p].beg, overlay.table[p].end, deleted );
+#endif
+	return;
+    }
+    // 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 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 region p => change p
+    // and handle any subsequent regions being covered
+    overlay.table[p].beg = beg;
+    q = p+1;
+    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_save_table( p, q );
+#if DEBUG
+    fprintf( stderr, "overlay before ( %ld %ld ) deleted %d\n",
+	     overlay.table[p].beg, overlay.table[p].end, deleted );
+#endif
+}
+
+/**
+ * Capture overlay filenames for processing after source fragments.
+ */
+static void overlay_setup(char *filenames) {
+    overlay.source.filename = filenames;
+}
+
+// Duplicate the source record data at the given index.
+static void dup_source_item(int index) {
+    sources.count++;
+    sources.array = realloc(
+	sources.array, sources.count * sizeof( struct Source ) );
+    if ( sources.array == 0 ) {
+	fprintf( stderr, "** OOM when expanding frament table\n" );
+	usage();
+    }
+    // copy elements from [index] to [count-1] one element down
+    size_t size = ( sources.count - index - 1 ) * sizeof( struct Source ); 
+    memmove( &sources.array[ index+1 ], &sources.array[ index ], size );
+}
+
 #if DEBUG
 static void print_source(struct Source *p) {
     fprintf( stderr, "%p { %s, %ld, %ld, %ld, %d }\n",
@@ -67,6 +308,93 @@ static int RANGE(int s,int n ) {
     return ( s == n ) && *(range+c) == 0;
 }
 
+static int setup_source(struct Source *p,char *frag) {
+    struct stat filestat;
+    // Open the fragment file rw if possible, else ro
+    // First try the fragment in full, thereafter with range appendix
+    if ( stat( frag, &filestat ) == 0 ) {
+	p->filename = strdup( frag );
+	range = 0;
+    } else {
+	range = strrchr( frag, '/' ); // last '/'
+	p->filename = range? strndup( frag, range - frag ) : frag;
+    }
+    p->fd = open( p->filename, O_RDWR );
+    int rdonly = 0;
+    if ( p->fd < 0 ) {
+	rdonly = 1;
+	p->fd = open( p->filename, O_RDONLY );
+    }
+    if ( p->fd < 0 ) {
+	perror( p->filename );
+	return 1; // Error return
+    }
+    if ( ( range != 0 ) && stat( p->filename, &filestat ) ) {
+	perror( p->filename );
+	return 1; 
+    }
+    if ( rdonly ) {
+	fprintf( stderr, "** %s opened read-only\n", p->filename );
+    }
+    p->from = 0;
+    if ( S_ISBLK( filestat.st_mode ) ) {
+	// Block devices report size differently:
+	if ( ioctl( p->fd, BLKGETSIZE64, &filestat.st_size ) < 0 ) {
+	    perror( p->filename );
+	}
+#if DEBUG
+	fprintf( stderr, "block device size = %ld\n", filestat.st_size );
+#endif
+    }
+    p->to = filestat.st_size;
+    // Process any range variation
+    if ( range && *(++range) ) {
+	long int a,b;
+	if ( 0 ) {
+	} else if ( RANGE( sscanf( range, "%ld:%ld%n", &a, &b, &c ), 2 )) {
+	    p->from = ( a < 0 )? ( p->to + a ) : a;
+	    p->to = ( b < 0 )? ( p->to + b ) : b;
+	} else if ( RANGE( sscanf( range, "%ld+%ld%n", &a, &b, &c ), 2 )) {
+	    p->from = ( a < 0 )? ( p->to + a ) : a;
+	    p->to = ( ( b < 0 )? p->to : p->from ) + b;
+	} else if ( RANGE( sscanf( range, "%ld+%n", &a, &c ), 1 )) {
+	    p->from = ( a < 0 )? ( p->to + a ) : a;
+	} else if ( RANGE( sscanf( range, ":%ld%n", &b, &c ), 1 )) {
+	    p->to = ( b < 0 )? ( p->to + b ) : b;
+	} else if ( RANGE( sscanf( range, "%ld:%n", &a, &c ), 1 )) {
+	    p->from = ( a < 0 )? ( p->to + a ) : a;
+	} else if ( RANGE( sscanf( range, "%ld%n", &a, &c ), 1 )) {
+	    if ( a >= 0 ) {
+		p->from = a;
+	    } else {
+		p->from = p->to + a;
+	    }
+	} else if ( RANGE( sscanf( range, ":%n", &c), 0 ) ) {
+	    // to end from start
+	} else {
+	    fprintf( stderr, "** BAD RANGE: %s\n", frag );
+	    return 1;
+	}
+    }
+    if ( ( filestat.st_mode &  S_IFMT ) == S_IFCHR ) {
+	filestat.st_size = p->to; // Pretend size of character device
+    }
+    if ( p->from < 0 ) {
+	p->from = 0;
+    }
+    if ( p->to > filestat.st_size ) {
+	p->to = filestat.st_size;
+    }
+    if ( p->from >= p->to || p->from >= filestat.st_size ) {
+	fprintf( stderr, "** BAD RANGE: %s [%ld:%ld]\n",
+		 frag, p->from, p->to );
+	return 1;
+    }
+    p->start = sources.size; // the fusefile position of fragment
+    sources.size += p->to - p->from;
+    return 0;
+}
+
 static int setup_sources(char **argv,int i,int n) {
     sources.array = calloc( n, sizeof( struct Source ) );
     if ( sources.array == 0 ) {
@@ -76,75 +404,10 @@ static int setup_sources(char **argv,int i,int n) {
     int j = 0;
     sources.size = 0;
     for ( ; j < n; i++, j++ ) {
-	struct stat filestat;
 	struct Source *p = sources.array + j;
-	// Open the fragment file rw if possible, else ro
-	range = strrchr( argv[i], '/' ); // last '/'
-	p->filename = range? strndup( argv[i], range - argv[i] ) : argv[i];
-	p->fd = open( p->filename, O_RDWR );
-	int rdonly = 0;
-	if ( p->fd < 0 ) {
-	    rdonly = 1;
-	    p->fd = open( p->filename, O_RDONLY );
-	}
-	if ( p->fd < 0 ) {
-	    perror( p->filename );
-	    return 1; // Error return
-	}
-	if ( stat( p->filename, &filestat ) ) {
-	    perror( p->filename );
-	    return 1; 
-	}
-	if ( rdonly ) {
-	    fprintf( stderr, "** %s opened read-only\n", p->filename );
-	}
-	p->from = 0;
-	p->to = filestat.st_size;
-	// Process any range variation
-	if ( range && *(++range) ) {
-	    int a,b;
-	    if ( 0 ) {
-	    } else if ( RANGE( sscanf( range, "%d:%d%n", &a, &b, &c ), 2 )) {
-		p->from = ( a < 0 )? ( p->to + a ) : a;
-		p->to = ( b < 0 )? ( p->to + b ) : b;
-	    } else if ( RANGE( sscanf( range, "%d+%d%n", &a, &b, &c ), 2 )) {
-		p->from = ( a < 0 )? ( p->to + a ) : a;
-		p->to = ( ( b < 0 )? p->to : p->from ) + b;
-	    } else if ( RANGE( sscanf( range, "%d+%n", &a, &c ), 1 )) {
-		p->from = ( a < 0 )? ( p->to + a ) : a;
-	    } else if ( RANGE( sscanf( range, ":%d%n", &b, &c ), 1 )) {
-		p->to = ( b < 0 )? ( p->to + b ) : b;
-	    } else if ( RANGE( sscanf( range, "%d:%n", &a, &c ), 1 )) {
-		p->from = ( a < 0 )? ( p->to + a ) : a;
-	    } else if ( RANGE( sscanf( range, "%d%n", &a, &c ), 1 )) {
-		if ( a >= 0 ) {
-		    p->from = a;
-		} else {
-		    p->from = p->to + a;
-		}
-	    } else if ( RANGE( sscanf( range, ":%n", &c), 0 ) ) {
-		// to end from start
-	    } else {
-		fprintf( stderr, "** BAD RANGE: %s\n", argv[i] );
-		return 1;
-	    }
-	}
-	if ( ( filestat.st_mode &  S_IFMT ) == S_IFCHR ) {
-	    filestat.st_size = p->to; // Pretend size of character device
-	}
-	if ( p->from < 0 ) {
-	    p->from = 0;
-	}
-	if ( p->to > filestat.st_size ) {
-	    p->to = filestat.st_size;
-	}
-	if ( p->from >= p->to || p->from >= filestat.st_size ) {
-	    fprintf( stderr, "** BAD RANGE: %s [%ld:%ld]\n",
-		     argv[i], p->from, p->to );
+	if ( setup_source( p, argv[i] ) ) {
 	    return 1;
 	}
-	p->start = sources.size; // the fusefile position of fragment
-	sources.size += p->to - p->from;
 #if DEBUG
 	print_source( p );
 #endif
@@ -200,79 +463,88 @@ static int find_source(off_t offset) {
     if ( offset >= sources.size ) {
 	return -1;
     }
-#if DEBUG
-    fprintf( stderr, "find_source( %ld )\n", offset );
-#endif
     while ( lo + 1 < hi ) {
 	int m = ( lo + hi ) / 2;
 	if ( offset < sources.array[ m ].start ) {
-#if DEBUG
-	    fprintf( stderr, "  offset < [%d].start: %ld\n",
-		     m, sources.array[ m ].start );
-#endif
 	    hi = m;
 	} else {
-#if DEBUG
-	    fprintf( stderr, "  offset >= [%d].start: %ld\n",
-		     m, sources.array[ m ].start );
-#endif
 	    lo = m;
 	}
     }
+    return lo;
+}
+
+static int overlay_merge(char *buf,off_t beg,off_t end) {
 #if DEBUG
-    fprintf( stderr, "found %d\n", lo );
+    fprintf( stderr, "merge %ld %ld\n", beg, end );
 #endif
-    return lo;
+    // Find nearest overlay data before or at beg
+    ssize_t p = overlay_prior_fragment( beg );
+    if ( p < 0 ) {
+	p = 0;
+    }
+    for ( ; p < overlay.count && overlay.table[p].beg < end; p++ ) {
+	if ( overlay.table[p].end < beg ) {
+	    continue;
+	}
+	if ( overlay.table[p].beg > beg ) {
+	    size_t delta = overlay.table[p].beg - beg;
+	    buf += delta;
+	    beg += delta;
+	}
+	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;
+	    buf += n;
+	    beg += n; //
+	}
+    }
+    return 0;
 }
 
 // Read <size> bytes from <offset> in file
 static int fusefile_read(const char *path, char *buf, size_t size,
 			 off_t off, struct fuse_file_info *fi)
 {
-#if DEBUG
-    fprintf( stderr, "fusefile_read( %s )\n", path );
-#endif
     if( strcmp( path, "/" ) != 0 ) {
 	return -ENOENT;
     }
-#if DEBUG
-    fprintf( stderr, "read %ld %ld\n", off, size );
-#endif
     size_t rr = 0; // total reading
-    while ( size > 0 ) {
 #if DEBUG
-	fprintf( stderr, "  find_source %ld %ld\n", off, size );
+    fprintf( stderr, "fusefile_read %ld + %ld\n", off, size );
 #endif
+    while ( size > 0 ) {
 	int i = find_source( off );
 	if ( i < 0 ) {
 	    return ( off == sources.size )? rr : -ENOENT;
 	}
+#if DEBUG
+	fprintf( stderr, " item: %d ", i );
+	print_source(& sources.array[i] );
+#endif
 	if ( sources.array[i].fd < 0 ) {
 	    return -ENOENT;
 	}
-#if DEBUG
-	print_source( &sources.array[i] );
-#endif
 	times.atime = time( 0 );
 	size_t b = off - sources.array[i].start + sources.array[i].from;
 	size_t n = sources.array[i].to - b;
 	if ( n > size ) {
 	    n = size;
 	}
-#if DEBUG
-	fprintf( stderr, "  seek fd=%d to %ld\n", sources.array[i].fd, b );
-#endif
+	if ( sources.array[i].dirty ) {
+	    fsync( sources.array[i].fd );
+	    sources.array[i].dirty = 0;
+	}
 	if ( lseek( sources.array[i].fd, b, SEEK_SET ) < 0 ) {
 	    perror( sources.array[i].filename );
 	    return -ENOENT;
 	}
-#if DEBUG
-	fprintf( stderr, "  now read %ld from fd=%d\n",
-		 n, sources.array[i].fd );
-#endif
 	ssize_t r = read( sources.array[i].fd, buf + rr, n );
 #if DEBUG
-	fprintf( stderr, "  got %ld bytes\n", r );
+	fprintf( stderr, " got: %ld bytes of %ld at %ld\n", r, n, rr );
 #endif
 	if ( r < 0 ) {
 	    perror( sources.array[i].filename );
@@ -281,6 +553,16 @@ static int fusefile_read(const char *path, char *buf, size_t size,
 	if ( r == 0 ) {
 	    break;
 	}
+	if ( overlay.source.filename ) {
+	    if ( overlay.source.dirty ) {
+		fsync( overlay.source.fd );
+		overlay.source.dirty = 0;
+	    }
+	    int x = overlay_merge( buf + rr, off + rr, off + rr + r );
+	    if ( x ) {
+		return x;
+	    }
+	}
 	rr += r;
 	off += r;
 	size -= r;
@@ -309,6 +591,169 @@ int fusefile_poll(const char *path, struct fuse_file_info *fi,
     return 0;
 }
 
+static void overlay_load() {
+    lseek( overlay.source.fd, overlay.source.to, SEEK_SET );
+    size_t x = 0;
+    size_t size = sizeof( overlay.count );
+    if ( read( overlay.source.fd, &x, size ) != size ) {
+	return;
+    }
+#if DEBUG
+    fprintf( stderr, "overlay: %s with %ld regions\n",
+	     overlay.source.filename, x );
+#endif
+    struct Region f = { 0, 0 };
+    size = sizeof( struct Region );
+    while ( x-- > 0 ) {
+	if ( read( overlay.source.fd, &f, size ) != size ) {
+	    fprintf( stderr, "%s: bad meta data\n", overlay.source.filename );
+	    exit( 1 );
+	}
+#if DEBUG
+	fprintf( stderr, "overlay region: %ld %ld\n", f.beg, f.end );
+#endif
+	overlay_mark( f.beg, f.end );
+    }
+}
+
+/**
+ * Inject an overlay fragment into the source table, end return the
+ * end of the injected fragment.
+ */
+static off_t overlay_inject_from_region(off_t beg,off_t end) {
+    int index = find_source( beg );
+    if ( index < 0 ) {
+	fprintf( stderr, "** Injecting %s at %ld failed\n",
+		 overlay.source.filename, beg );
+	usage();
+    }
+    if ( end > ENDSOURCE( sources.array[ index ] ) ) {
+	end = ENDSOURCE( sources.array[ index ] );
+    }
+    struct Region frags[3] = {
+	{ sources.array[ index ].start, beg },
+	{ beg, end },
+	{ end, ENDSOURCE( sources.array[ index ] ) } };
+#if DEBUG
+    int i;
+    for ( i = 0; i < 3; i++ ) {
+	fprintf( stderr, "frags[%d] = (%ld, %ld)\n",
+		 i, frags[i].beg, frags[i].end );
+    }
+#endif
+    ssize_t size = frags[0].end - frags[0].beg;
+    if ( size ) {
+	// Handle any portion before injection point.
+	dup_source_item( index );
+	off_t point = sources.array[ index ].from + size;
+	sources.array[ index ].to = point;
+#if DEBUG
+	fprintf( stderr, "item %d ", index );
+	print_source( &sources.array[ index ] );
+#endif
+	// Adjust item after injection point
+	index++;
+	sources.array[ index ].start = beg;
+	sources.array[ index ].from = point;
+#if DEBUG
+	fprintf( stderr, "item %d adjust ", index );
+	print_source( &sources.array[ index ] );
+#endif
+    }
+    size = frags[2].end	- frags[2].beg;
+    if ( size ) {
+	// Handle any remaining portion following injection fragment
+	dup_source_item( index );
+	sources.array[ index+1 ].start = frags[2].beg;
+	sources.array[ index+1 ].from += frags[1].end - frags[1].beg;
+#if DEBUG
+	fprintf( stderr, "item %d ", index+1 );
+	print_source( &sources.array[ index+1 ] );
+#endif
+    }
+    // Set up the injection fragment
+    sources.array[ index ].filename = overlay.source.filename;
+    sources.array[ index ].from = beg;
+    sources.array[ index ].to = end;
+    sources.array[ index ].fd = overlay.source.fd;
+#if DEBUG
+	fprintf( stderr, "item %d ", index );
+	print_source( &sources.array[ index ] );
+#endif
+    return end;
+}
+
+/**
+ * Inject the current (unopened) overlay into the source list.
+ */
+static void overlay_inject() {
+    overlay.source.fd = open( overlay.source.filename, O_RDONLY );
+    if ( overlay.source.fd < 0 ) {
+	perror( overlay.source.filename );
+	usage();
+    }
+    
+    if ( lseek( overlay.source.fd, overlay.source.to, SEEK_SET ) < 0 ) {
+	perror( overlay.source.filename );
+	usage();
+    }
+    size_t count = 0;
+    size_t size = sizeof( overlay.count );
+    size_t n;
+    if ( ( n = read( overlay.source.fd, &count, size ) ) != size ) {
+	if ( n != 0 ) {
+	    fprintf( stderr, "** error injecting %s\n",
+		     overlay.source.filename );
+	    usage();
+	}
+	fprintf( stderr, "** ignoring empty %s\n", overlay.source.filename );
+    }
+    if ( count == 0 ) {
+	close( overlay.source.fd );
+	return;
+    }
+    size = count * sizeof( struct Region );
+    overlay.table = calloc( sizeof( struct Region ), count );
+    if ( read( overlay.source.fd, overlay.table, size ) != size ) {
+	fprintf( stderr, "** error injecting %s\n", overlay.source.filename );
+	usage();
+    }
+    size_t i;
+    for ( i = 0; i < count; i++ ) {
+	off_t beg = overlay.table[i].beg;
+	while ( beg < overlay.table[i].end ) {
+#if DEBUG
+	    fprintf( stderr, "inject [%ld,%ld] ", beg, overlay.table[i].end );
+	    print_source( &overlay.source );
+#endif
+	    
+	    beg = overlay_inject_from_region( beg, overlay.table[i].end );
+	}
+    }
+    free( overlay.table );
+    overlay.table = 0;
+}
+
+/**
+ * Each stacked overlay file is nested into to source list
+ */
+static void overlay_post_setup() {
+    char *end;
+    while ( ( end = strchr( overlay.source.filename, ':' ) ) ) {
+	*end = 0; //
+	overlay_inject();
+	overlay.source.filename = end + 1;
+    }
+    if ( *overlay.source.filename ) {
+	overlay.source.fd = open( overlay.source.filename,
+				  O_RDWR | O_CREAT, S_IRUSR | S_IWUSR );
+	if ( overlay.source.fd < 0 ) {
+	    perror( overlay.source.filename );
+	    usage();
+	}
+	overlay_load();
+    }
+}
 
 /**
  * Write a full block of data over the sources at the offset
@@ -317,12 +762,16 @@ static int write_block(off_t off,const char *buf,size_t size) {
 #if DEBUG
     fprintf( stderr, "write_block( %ld, ?, %ld )\n", off, size );
 #endif
+    if ( overlay.source.filename ) {
+	overlay_mark( off, off + size ); // Mark region as written
+    }
     while ( size > 0 ) {
 	int index = find_source( off ); // index of source file
 	if ( index < 0 ) {
 	    return -EIO; // past EOF
 	}
-	struct Source *source = &sources.array[ index ];
+	struct Source *source = overlay.source.filename?
+	    &overlay.source :  &sources.array[ index ];
 	off_t from = off - source->start + source->from;
 	off_t max = source->to - from;
 	if ( lseek( source->fd, from, SEEK_SET ) < 0 ) {
@@ -340,6 +789,10 @@ static int write_block(off_t off,const char *buf,size_t size) {
 	    size -= n;
 	    off += n;
 	}
+	if ( source->dirty++ >= 1000 ) {
+	    fsync( source->fd );
+	    source->dirty = 0;
+	}
     }
     return 0;
 }
@@ -352,7 +805,6 @@ static int fusefile_write_buf(const char *path, struct fuse_bufvec *buf,
     if ( strcmp( path, "/" ) != 0 ) {
 	return -ENOENT;
     }
-
     size_t size = 0;
     int i;
     for ( i = 0; i < buf->count; i++ ) {
@@ -393,6 +845,40 @@ static int fusefile_write(const char *path, const char *buf, size_t size,
     return size;
 }
 
+#define PUSHBUF 104857600
+/**
+ * Write data from overlay to source.
+ */
+static void push_oly(off_t beg, off_t end) {
+    static char * buffer = 0;
+    // Pretend that there isn't an overlay
+    char *filename = overlay.source.filename;
+    if ( buffer == 0 ) {
+	buffer = malloc( PUSHBUF );
+	if ( buffer == 0 ) {
+	    fprintf( stderr, "** OOM!!\n" );
+	    exit( 1 );
+	}
+    }
+    overlay.source.filename = 0;
+    while ( beg < end ) {
+	off_t size = end - beg;
+	if ( size > PUSHBUF ) {
+	    size = PUSHBUF;
+	}
+	if ( lseek( overlay.source.fd, beg, SEEK_SET ) < 0 ) {
+	    fprintf( stderr, "** Cannot seek overlay at %ld\n", beg );
+	    break;
+	}
+	size = read( overlay.source.fd, buffer, size );
+	if ( write_block( beg, buffer, size ) < 0 ) {
+	    fprintf( stderr, "** Cannot push %ld bytes at %ld\n", size, beg );
+	}
+	beg += size;
+    }
+    overlay.source.filename = filename;
+}
+
 static void fusefile_destroy(void *data) {
     char *mnt = (char*) data; // As passed to fuse_main
 #if DEBUG
@@ -403,6 +889,20 @@ static void fusefile_destroy(void *data) {
     }
 }
 
+static void fsync_all_dirty() {
+    int i = 0;
+    for ( ; i < sources.count; i++ ) {
+	if ( sources.array[i].dirty ) {
+	    fsync( sources.array[i].fd );
+	    sources.array[i].dirty = 0;
+	}
+    }
+    if ( overlay.source.filename && overlay.source.dirty ) {
+	fsync( overlay.source.fd );
+	overlay.source.dirty = 0;
+    }
+}
+
 static int fusefile_flush(const char *path, struct fuse_file_info *info) {
 #if DEBUG
     fprintf( stderr, "fusefile_flush( %s )\n", path );
@@ -410,6 +910,7 @@ static int fusefile_flush(const char *path, struct fuse_file_info *info) {
     if ( strcmp( path, "/" ) != 0 ) {
 	return -ENOENT;
     }
+    fsync_all_dirty();
     return 0;
 }
 
@@ -430,6 +931,7 @@ static int fusefile_fsync(const char *path, int x, struct fuse_file_info *fi) {
     if ( strcmp( path, "/" ) != 0 ) {
 	return -ENOENT;
     }
+    fsync_all_dirty();
     return 0;
 }
 
@@ -459,8 +961,63 @@ void *fusefile_init(struct fuse_conn_info *fci) {
     return 0;
 }
 
+/**
+ * Dump the current fragmentation to stdout.
+ */
+static int dump_fragments(int push) {
+    int oly = 0;
+    int src = 0;
+    size_t pos = 0;
+    while ( src < sources.count ) {
+	size_t x = ( oly < overlay.count )?
+	    overlay.table[ oly ].beg : sources.size;
+	for ( ; src < sources.count && 
+		  ENDSOURCE( sources.array[ src ] ) <= x; src++ ) {
+	    // Dump sources.array[src] in full
+	    if ( !push ) {
+		fprintf( stdout, "%s/%ld:%ld\n",
+			 sources.array[ src ].filename,
+			 pos - sources.array[ src ].start +
+			 sources.array[ src ].from,
+			 sources.array[ src ].to );
+	    }
+	    pos = ENDSOURCE( sources.array[ src ] );
+	}
+	if ( ( src < sources.count ) && ( sources.array[ src ].start < x ) ) {
+	    // Dump sources.array[src] up to x;
+	    if ( !push ) {
+		fprintf( stdout, "%s/%ld:%ld\n",
+			 sources.array[ src ].filename,
+			 sources.array[ src ].from +
+			 pos - sources.array[ src ].start,
+			 x - sources.array[ src ].start +
+			 sources.array[ src ].from
+			 );
+	    }
+	    pos = ENDSOURCE( sources.array[ src ] );
+	}
+	if ( oly < overlay.count ) {
+	    if ( !push ) {
+		fprintf( stdout, "%s/%ld:%ld\n",
+			 overlay.source.filename,
+			 overlay.table[ oly ].beg,
+			 overlay.table[ oly ].end );
+	    } else {
+		push_oly( overlay.table[ oly ].beg, overlay.table[ oly ].end );
+	    }
+	    pos = overlay.table[ oly++ ].end;
+	}
+	for ( ; src < sources.count &&
+		  ENDSOURCE( sources.array[ src ] ) <= pos; src++ ) {
+	    // Just skip these fragments.
+	}
+    }
+    return( 0 );
+}
+
 static struct fuse_operations fusefile_oper = {
     .getattr = fusefile_getattr,
+    // NYI .fgetattr = fusefile_fgetattr,
     .chmod = fusefile_chmod,
     .open = fusefile_open,
     .read = fusefile_read,
@@ -468,9 +1025,11 @@ static struct fuse_operations fusefile_oper = {
     .write = fusefile_write,
     .write_buf = fusefile_write_buf,
     .destroy = fusefile_destroy,
+    // NYI .access = fusefile_access,
     .flush = fusefile_flush,
     .release = fusefile_release,
     .fsync = fusefile_fsync,
+    // NYI .ftruncate = fusefile_ftruncate,
     .truncate = fusefile_truncate,
     //.truncate = fusefile_truncate,
     //.release = fusefile_release,
@@ -494,6 +1053,7 @@ static int setup_argv(int argc,char ***argv) {
     // note: (*argv)[ argc ] is the mount point argument
     char *OURS[] = {
 	"-odefault_permissions",
+	//"-s", // Forced single-threading
 	(*argv)[ argc ]
     };
 #define OURSN ( sizeof( OURS ) / sizeof( char* ) )
@@ -539,9 +1099,21 @@ int main(int argc, char *argv[])
     }
     fuseargc = i;
     mnt = argv[ i++ ]; // First non-option argument is the mount pount
+    #define OVERLAYTAG "-overlay:"
+    if ( strncmp( argv[i], OVERLAYTAG, strlen( OVERLAYTAG ) ) == 0 ) {
+	// consume "-overlay:filename[,filename]*"
+	overlay_setup( argv[i++] + strlen( OVERLAYTAG ) );
+	if ( i >= argc ) {
+	    usage();
+	}
+    }
     if ( setup_sources( argv, i, argc-i ) ) {
 	return 1;
     }
+    if ( overlay.source.filename ) {
+	overlay.source.to = sources.size; // Register total size.
+	overlay_post_setup();
+    }
     if ( stat( mnt, &stbuf ) == -1 ) {
 	int fd = open( mnt, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR );
 	if ( fd < 0 ) {
@@ -574,6 +1146,12 @@ int main(int argc, char *argv[])
 	}
     }
     fuseargc = setup_argv( fuseargc, &argv );
+    if ( strcmp( "-dump", argv[ 1 ] ) == 0 ) {
+	return dump_fragments( 0 );
+    }
+    if ( strcmp( "-push", argv[ 1 ] ) == 0 ) {
+	return dump_fragments( 1 );
+    }
     struct fuse_args args = FUSE_ARGS_INIT( fuseargc, argv );
     if ( fuse_parse_cmdline( &args, &mnt, &mt, &fg ) ) {
 	return 1;