3 files changed, 145 insertions, 19 deletions

diff --git a/firmware/common/file.c b/firmware/common/file.c
index 41aaea570a..a5d9443aeb 100644
--- a/firmware/common/file.c
+++ b/firmware/common/file.c
@@ -100,7 +100,7 @@ int open(char* pathname, int flags)
         return -1;
     }
 
-    openfiles[fd].cacheoffset = 0;
+    openfiles[fd].cacheoffset = -1;
     openfiles[fd].fileoffset = 0;
     openfiles[fd].busy = TRUE;
     return fd;
@@ -127,7 +127,7 @@ int read(int fd, void* buf, int count)
         count = openfiles[fd].size - openfiles[fd].fileoffset;
 
     /* any head bytes? */
-    if ( openfiles[fd].cacheoffset ) {
+    if ( openfiles[fd].cacheoffset != -1 ) {
         int headbytes;
         int offs = openfiles[fd].cacheoffset;
         if ( count <= SECTOR_SIZE - openfiles[fd].cacheoffset ) {
@@ -138,7 +138,7 @@ int read(int fd, void* buf, int count)
         }
         else {
             headbytes = SECTOR_SIZE - openfiles[fd].cacheoffset;
-            openfiles[fd].cacheoffset = 0;
+            openfiles[fd].cacheoffset = -1;
         }
 
         /* eof? */
@@ -169,7 +169,7 @@ int read(int fd, void* buf, int count)
                 count=0;
             }
 
-            openfiles[fd].cacheoffset = 0;
+            openfiles[fd].cacheoffset = -1;
         }
     }
 
@@ -195,6 +195,70 @@ int read(int fd, void* buf, int count)
     return nread;
 }
 
+int lseek(int fd, int offset, int whence)
+{
+    int pos;
+    int newsector;
+    int oldsector;
+    int sectoroffset;
+    int rc;
+
+    if ( !openfiles[fd].busy ) {
+        errno = EBADF;
+        return -1;
+    }
+
+    switch ( whence ) {
+        case SEEK_SET:
+            pos = offset;
+            break;
+
+        case SEEK_CUR:
+            pos = openfiles[fd].fileoffset + offset;
+            break;
+
+        case SEEK_END:
+            pos = openfiles[fd].size - offset;
+            break;
+
+        default:
+            errno = EINVAL;
+            return -1;
+    }
+    if ( (pos < 0) ||
+         (pos > openfiles[fd].size) ) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    /* new sector? */
+    newsector = pos / SECTOR_SIZE;
+    oldsector = openfiles[fd].fileoffset / SECTOR_SIZE;
+    sectoroffset = pos % SECTOR_SIZE;
+
+    if ( (newsector != oldsector) ||
+         ((openfiles[fd].cacheoffset==-1) && sectoroffset) ) {
+        if ( newsector != oldsector ) {
+            rc = fat_seek(&(openfiles[fd].fatfile), newsector);
+            if ( rc < 0 ) {
+                errno = EIO;
+                return -1;
+            }
+        }
+        rc = fat_read(&(openfiles[fd].fatfile), 1,
+                      &(openfiles[fd].cache));
+        if ( rc < 0 ) {
+            errno = EIO;
+            return -1;
+        }
+    }
+
+    openfiles[fd].cacheoffset = sectoroffset;
+    openfiles[fd].fileoffset = pos;
+
+    return pos;
+}
+
 /*
  * local variables:
  * eval: (load-file "../rockbox-mode.el")
diff --git a/firmware/drivers/fat.c b/firmware/drivers/fat.c
index 3a3f63d9f1..a55a8a2864 100644
--- a/firmware/drivers/fat.c
+++ b/firmware/drivers/fat.c
@@ -838,22 +838,30 @@ int fat_seek(struct fat_file *file, int seeksector )
     int numsec = 0;
     int i;
 
-    for (i=0; i<seeksector; i++) {
-        numsec++;
-        if ( numsec >= fat_bpb.bpb_secperclus ) {
-            cluster = get_next_cluster(cluster);
-            if (!cluster)
-                /* end of file */
-                return -1; 
-            
-            sector = cluster2sec(cluster);
-            if (sector<0)
-                return -2;
-            numsec=0;
+    if ( seeksector ) {
+        for (i=0; i<seeksector; i++) {
+            numsec++;
+            if ( numsec >= fat_bpb.bpb_secperclus ) {
+                cluster = get_next_cluster(cluster);
+                if (!cluster)
+                    /* end of file */
+                    return -1; 
+                
+                sector = cluster2sec(cluster);
+                if (sector<0)
+                    return -2;
+                numsec=0;
+            }
+            else
+                sector++;
         }
-        else
-          sector++;
     }
+    else {
+        sector = cluster2sec(cluster);
+        if (sector<0)
+            return -2;
+    }
+        
     file->nextcluster = cluster;
     file->nextsector = sector;
     file->sectornum = numsec;
diff --git a/firmware/test/fat/main.c b/firmware/test/fat/main.c
index 5490fa9777..6d05dbe600 100644
--- a/firmware/test/fat/main.c
+++ b/firmware/test/fat/main.c
@@ -129,6 +129,59 @@ void dbg_type(char* name)
     close(fd);
 }
 
+void dbg_tail(char* name)
+{
+    unsigned char buf[SECTOR_SIZE*5];
+    int fd,rc;
+
+    fd = open(name,O_RDONLY);
+    if (fd<0)
+        return;
+    DEBUGF("Got file descriptor %d\n",fd);
+    
+    rc = lseek(fd,512,SEEK_SET);
+    if ( rc >= 0 ) {
+        rc = read(fd, buf, SECTOR_SIZE);
+        if( rc > 0 )
+        {
+            buf[rc]=0;
+            printf("%d: %s\n", strlen(buf), buf);
+        }
+        else if ( rc == 0 ) {
+            DEBUGF("EOF\n");
+        }
+        else
+        {
+            DEBUGF("Failed reading file: %d\n",rc);
+        }
+    }
+    else {
+        perror("lseek");
+    }
+
+    rc = lseek(fd,-100,SEEK_CUR);
+    if ( rc >= 0 ) {
+        rc = read(fd, buf, SECTOR_SIZE);
+        if( rc > 0 )
+        {
+            buf[rc]=0;
+            printf("%d: %s\n", strlen(buf), buf);
+        }
+        else if ( rc == 0 ) {
+            DEBUGF("EOF\n");
+        }
+        else
+        {
+            DEBUGF("Failed reading file: %d\n",rc);
+        }
+    }
+    else {
+        perror("lseek");
+    }
+
+    close(fd);
+}
+
 char current_directory[256] = "\\";
 int last_secnum = 0;
 
@@ -221,7 +274,8 @@ int main(int argc, char *argv[])
         DEBUGF("*** Failed mounting fat\n");
     }
 
-    dbg_console();
+    //dbg_console();
+    dbg_tail("/fat.h");
 
     return 0;
 }