WebSVN – HelenOS – Diff – /branches/dynload/uspace/srv/fs/fat/fat_fat.c

  * during allocation of clusters. The lock does not have to be held durring
  * deallocation of clusters.
  */
 static futex_t fat_alloc_lock = FUTEX_INITIALIZER;
-/** Read block from file located on a FAT file system.
+/** Walk the cluster chain.
+ *
- * @param bs        Buffer holding the boot sector of the file system.
+ * @param bs        Buffer holding the boot sector for the file.
- * @param dev_handle    Device handle of the file system.
+ * @param dev_handle    Device handle of the device with the file.
- * @param firstc    First cluster used by the file. Can be zero if the file
+ * @param firstc    First cluster to start the walk with.
+ * @param penult    If non-NULL, output argument hodling the
+ *          the penultimate cluster visited.
+ * @param ult       If non-NULL, output argument holding the
- *          is empty.
+ *          ultimate cluster visited.
- * @param offset    Offset in blocks.
+ * @param max_clusters  Maximum number of clusters to visit.
+ *
- * @return      Block structure holding the requested block.
+ * @return      Number of clusters seen during the walk.
  */
-block_t *
+uint16_t
-_fat_block_get(fat_bs_t *bs, dev_handle_t dev_handle, fat_cluster_t firstc,
+fat_cluster_walk(fat_bs_t *bs, dev_handle_t dev_handle, fat_cluster_t firstc,
-    off_t offset)
+    fat_cluster_t *penult, fat_cluster_t *ult, uint16_t max_clusters)
+{
     block_t *b;
     unsigned bps;
-    unsigned spc;
     unsigned rscnt;     /* block address of the first FAT */
-    unsigned fatcnt;
-    unsigned rde;
-    unsigned rds;       /* root directory size */
-    unsigned sf;
-    unsigned ssa;       /* size of the system area */
-    unsigned clusters;
+    uint16_t clusters = 0;
     fat_cluster_t clst = firstc;
-    unsigned i;
     bps = uint16_t_le2host(bs->bps);
-    spc = bs->spc;
     rscnt = uint16_t_le2host(bs->rscnt);
-    fatcnt = bs->fatcnt;
-    rde = uint16_t_le2host(bs->root_ent_max);
-    sf = uint16_t_le2host(bs->sec_per_fat);
-    rds = (sizeof(fat_dentry_t) * rde) / bps;
-    rds += ((sizeof(fat_dentry_t) * rde) % bps != 0);
-    ssa = rscnt + fatcnt * sf + rds;
-    if (firstc == FAT_CLST_ROOT) {
+    if (firstc == FAT_CLST_RES0) {
-        /* root directory special case */
+        /* No space allocated to the file. */
-        assert(offset < rds);
+        if (ult)
-        b = block_get(dev_handle, rscnt + fatcnt * sf + offset, bps);
+            *ult = firstc;
-        return b;
+        return 0;
+    }
+    /* At this point, the meaning of penult is not well-defined. */
+    if (penult)
-    clusters = offset / spc;
+        *penult = FAT_CLST_RES0;
-    for (i = 0; i < clusters; i++) {
+    while (clst < FAT_CLST_LAST1 && clusters < max_clusters) {
         unsigned fsec;  /* sector offset relative to FAT1 */
         unsigned fidx;  /* FAT1 entry index */
-        assert(clst >= FAT_CLST_FIRST && clst < FAT_CLST_BAD);
+        assert(clst >= FAT_CLST_FIRST);
+        if (penult)
+            *penult = clst; /* remember the penultimate cluster */
         fsec = (clst * sizeof(fat_cluster_t)) / bps;
         fidx = clst % (bps / sizeof(fat_cluster_t));
         /* read FAT1 */
-        b = block_get(dev_handle, rscnt + fsec, bps);
+        b = block_get(dev_handle, rscnt + fsec);
         clst = uint16_t_le2host(((fat_cluster_t *)b->data)[fidx]);
         assert(clst != FAT_CLST_BAD);
-        assert(clst < FAT_CLST_LAST1);
         block_put(b);
+        clusters++;
+    }
-    b = block_get(dev_handle, ssa + (clst - FAT_CLST_FIRST) * spc +
+    if (ult)
-        offset % spc, bps);
+        *ult = clst;
-    return b;
+    return clusters;
+}
-/** Return number of blocks allocated to a file.
+/** Read block from file located on a FAT file system.
+ *
- * @param bs        Buffer holding the boot sector for the file.
+ * @param bs        Buffer holding the boot sector of the file system.
- * @param dev_handle    Device handle of the device with the file.
+ * @param dev_handle    Device handle of the file system.
- * @param firstc    First cluster of the file.
+ * @param firstc    First cluster used by the file. Can be zero if the file
- * @param lastc     If non-NULL, output argument holding the
- *          last cluster.
+ *          is empty.
+ * @param offset    Offset in blocks.
+ *
- * @return      Number of blocks allocated to the file.
+ * @return      Block structure holding the requested block.
  */
-uint16_t
+block_t *
-_fat_blcks_get(fat_bs_t *bs, dev_handle_t dev_handle, fat_cluster_t firstc,
+_fat_block_get(fat_bs_t *bs, dev_handle_t dev_handle, fat_cluster_t firstc,
-    fat_cluster_t *lastc)
+    off_t offset)
+{
     block_t *b;
     unsigned bps;
-    unsigned spc;
     unsigned rscnt;     /* block address of the first FAT */
+    unsigned rde;
+    unsigned rds;       /* root directory size */
+    unsigned sf;
+    unsigned ssa;       /* size of the system area */
-    unsigned clusters = 0;
+    unsigned clusters, max_clusters;
-    fat_cluster_t clst = firstc;
+    fat_cluster_t lastc, clst = firstc;
     bps = uint16_t_le2host(bs->bps);
-    spc = bs->spc;
     rscnt = uint16_t_le2host(bs->rscnt);
+    rde = uint16_t_le2host(bs->root_ent_max);
+    sf = uint16_t_le2host(bs->sec_per_fat);
+    rds = (sizeof(fat_dentry_t) * rde) / bps;
+    rds += ((sizeof(fat_dentry_t) * rde) % bps != 0);
+    ssa = rscnt + bs->fatcnt * sf + rds;
-    if (firstc == FAT_CLST_RES0) {
+    if (firstc == FAT_CLST_ROOT) {
-        /* No space allocated to the file. */
+        /* root directory special case */
-        if (lastc)
+        assert(offset < rds);
-            *lastc = firstc;
+        b = block_get(dev_handle, rscnt + bs->fatcnt * sf + offset);
-        return 0;
+        return b;
+    }
-    while (clst < FAT_CLST_LAST1) {
+    max_clusters = offset / bs->spc;
-        unsigned fsec;  /* sector offset relative to FAT1 */
+    clusters = fat_cluster_walk(bs, dev_handle, firstc, NULL, &lastc,
+        max_clusters);
-        unsigned fidx;  /* FAT1 entry index */
+    assert(clusters == max_clusters);
-        assert(clst >= FAT_CLST_FIRST);
-        if (lastc)
-            *lastc = clst;      /* remember the last cluster */
-        fsec = (clst * sizeof(fat_cluster_t)) / bps;
-        fidx = clst % (bps / sizeof(fat_cluster_t));
-        /* read FAT1 */
-        b = block_get(dev_handle, rscnt + fsec, bps);
+    b = block_get(dev_handle, ssa + (lastc - FAT_CLST_FIRST) * bs->spc +
-        clst = uint16_t_le2host(((fat_cluster_t *)b->data)[fidx]);
-        assert(clst != FAT_CLST_BAD);
-        block_put(b);
+        offset % bs->spc);
-        clusters++;
-    }
-    if (lastc)
-        *lastc = clst;
-    return clusters * spc;
+    return b;
+}
 /** Fill the gap between EOF and a new file position.
+ *
  * @param bs        Buffer holding the boot sector for nodep.
  * @param nodep     FAT node with the gap.
  * @param mcl       First cluster in an independent cluster chain that will
     rscnt = uint16_t_le2host(bs->rscnt);
     sf = uint16_t_le2host(bs->sec_per_fat);
     assert(fatno < bs->fatcnt);
     b = block_get(dev_handle, rscnt + sf * fatno +
-        (clst * sizeof(fat_cluster_t)) / bps, bps);
+        (clst * sizeof(fat_cluster_t)) / bps);
     cp = (fat_cluster_t *)b->data + clst % (bps / sizeof(fat_cluster_t));
     *cp = host2uint16_t_le(value);
     b->dirty = true;        /* need to sync block */
     block_put(b);
+}
     /*
      * Search FAT1 for unused clusters.
      */
     futex_down(&fat_alloc_lock);
     for (b = 0, cl = 0; b < sf; blk++) {
-        blk = block_get(dev_handle, rscnt + b, bps);
+        blk = block_get(dev_handle, rscnt + b);
         for (c = 0; c < bps / sizeof(fat_cluster_t); c++, cl++) {
             fat_cluster_t *clst = (fat_cluster_t *)blk->data + c;
             if (uint16_t_le2host(*clst) == FAT_CLST_RES0) {
                 /*
                  * The cluster is free. Put it into our stack
+{
     dev_handle_t dev_handle = nodep->idx->dev_handle;
     fat_cluster_t lcl;
     uint8_t fatno;
-    if (_fat_blcks_get(bs, dev_handle, nodep->firstc, &lcl) == 0) {
+    if (fat_cluster_walk(bs, nodep->idx->dev_handle, nodep->firstc, &lcl,
+        NULL, (uint16_t) -1) == 0) {
+        /* No clusters allocated to the node yet. */
         nodep->firstc = host2uint16_t_le(mcl);
         nodep->dirty = true;        /* need to sync node */
         return;
+    }

Subversion Repositories HelenOS

(root)/branches/dynload/uspace/srv/fs/fat/fat_fat.c @ 3578 – Rev 3535 → 3561