From: Ralph Ronnquist <ralph.ronnquist@gmail.com>
Date: Sun, 7 Aug 2022 07:06:49 +0000 (+1000)
Subject: added overlay option
X-Git-Tag: 0.5~4
X-Git-Url: https://git.rrq.au/?a=commitdiff_plain;h=a31db9efc8aa6da6cffecf4cff409730e96cbb86;p=rrq%2Ffusefile.git

added overlay option
---

diff --git a/fusefile.c b/fusefile.c
index 59dcaa5..8371d1f 100644
--- a/fusefile.c
+++ b/fusefile.c
@@ -53,7 +53,9 @@ static struct {
     time_t mtime;
     time_t ctime;
 } times;
-    
+
+static struct Source overlay;
+
 #if DEBUG
 static void print_source(struct Source *p) {
     fprintf( stderr, "%p { %s, %ld, %ld, %ld, %d }\n",
@@ -67,6 +69,17 @@ static int RANGE(int s,int n ) {
     return ( s == n ) && *(range+c) == 0;
 }
 
+static void usage();
+
+static void setup_overlay(char *filename) {
+    overlay.filename = filename;
+    overlay.fd = open( filename, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR );
+    if ( overlay.fd < 0 ) {
+	perror( filename );
+	usage();
+    }
+}
+
 static int setup_sources(char **argv,int i,int n) {
     sources.array = calloc( n, sizeof( struct Source ) );
     if ( sources.array == 0 ) {
@@ -225,6 +238,53 @@ static int find_source(off_t offset) {
     return lo;
 }
 
+#define OBUFSZ 1048576
+static int overlay_merge(char *buf,off_t off,size_t size) {
+    static char obuf[ OBUFSZ ];
+#if DEBUG
+    fprintf( stderr, "merge %ld %ld\n", off, size );
+#endif
+    while ( size > 0 ) {
+	size_t n = size < OBUFSZ? size : OBUFSZ;
+	off_t ox = lseek( overlay.fd, off, SEEK_SET );
+#if DEBUG
+	fprintf( stderr, "  seek %ld %ld %ld\n", off, ox, n );
+#endif
+	if ( ox < 0 ) {
+	    perror( overlay.filename );
+	    return -ENOENT;
+	}
+	if ( ox < off ) {
+	    break;
+	}
+	n = read( overlay.fd, obuf, n );
+#if DEBUG
+	fprintf( stderr, "  got %ld\n", n );
+#endif
+	if ( n < 0 ) {
+	    perror( overlay.filename );
+            return -ENOENT;
+	}
+	if ( n == 0 ) {
+	    break;
+	}
+	char *p = obuf;
+	while ( n-- > 0 ) {
+	    if ( *p ) {
+		*buf = *p;
+	    }
+	    p++;
+	    buf++;
+	    size--;
+	    off++;
+	}
+    }
+#if DEBUG
+    fprintf( stderr, "merged\n" );
+#endif
+    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)
@@ -271,6 +331,12 @@ static int fusefile_read(const char *path, char *buf, size_t size,
 		 n, sources.array[i].fd );
 #endif
 	ssize_t r = read( sources.array[i].fd, buf + rr, n );
+	if ( overlay.filename ) {
+	    int x = overlay_merge( buf + rr, off + rr, r );
+	    if ( x ) {
+		return x;
+	    }
+	}
 #if DEBUG
 	fprintf( stderr, "  got %ld bytes\n", r );
 #endif
@@ -322,7 +388,8 @@ static int write_block(off_t off,const char *buf,size_t size) {
 	if ( index < 0 ) {
 	    return -EIO; // past EOF
 	}
-	struct Source *source = &sources.array[ index ];
+	struct Source *source =
+	    overlay.filename? &overlay : &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 ) {
@@ -539,9 +606,19 @@ int main(int argc, char *argv[])
     }
     fuseargc = i;
     mnt = argv[ i++ ]; // First non-option argument is the mount pount
+    char *overlaytag = "-overlay:";
+    int overlaytagsize = strlen( overlaytag );
+    if ( strncmp( argv[i], overlaytag, overlaytagsize ) == 0 ) {
+	// consume "-overlay:filename"
+	setup_overlay( argv[i++] + overlaytagsize ); // Need a writable file
+	if ( i >= argc ) {
+	    usage();
+	}
+    }
     if ( setup_sources( argv, i, argc-i ) ) {
 	return 1;
     }
+    overlay.to = sources.size; // Register total size.
     if ( stat( mnt, &stbuf ) == -1 ) {
 	int fd = open( mnt, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR );
 	if ( fd < 0 ) {