+ BattFsPageHeader curr_hdr;
+ pgcnt_t new_page;
+
+ if (fd->seek_pos < 0)
+ {
+ fdb->errors |= BATTFS_NEGATIVE_SEEK_ERR;
+ return total_write;
+ }
+
+ if (fd->seek_pos > fd->size)
+ {
+ if (!readHdr(disk, fdb->start[fdb->max_off], &curr_hdr))
+ {
+ fdb->errors |= BATTFS_DISK_READ_ERR;
+ return total_write;
+ }
+
+ /*
+ * Renew page only if is not in cache.
+ * This avoids rewriting the same page continuously
+ * if the user code keeps writing in the same portion
+ * of the file.
+ */
+ if ((fdb->start[fdb->max_off] != kblock_cachedBlock(disk->dev)) || !kblock_cacheDirty(disk->dev))
+ {
+ new_page = renewPage(disk, fdb->start[fdb->max_off]);
+ if (new_page == NO_SPACE)
+ {
+ fdb->errors |= BATTFS_DISK_SPACEOVER_ERR;
+ return total_write;
+ }
+
+ kblock_copy(disk->dev, fdb->start[fdb->max_off], new_page);
+ fdb->start[fdb->max_off] = new_page;
+ }
+ else
+ new_page = fdb->start[fdb->max_off];
+
+ /* Fill unused space of first page with 0s */
+ uint8_t dummy = 0;
+ // TODO: write in blocks to speed up things
+ pgaddr_t zero_bytes = MIN(fd->seek_pos - fd->size, (kfile_off_t)(disk->data_size - curr_hdr.fill));
+ while (zero_bytes--)
+ {
+ if (kblock_write(disk->dev, new_page, &dummy, curr_hdr.fill, 1) != 1)
+ {
+ fdb->errors |= BATTFS_DISK_WRITE_ERR;
+ return total_write;
+ }
+ curr_hdr.fill++;
+ fd->size++;
+ disk->free_bytes--;
+ }
+ curr_hdr.seq++;
+ if (!writeHdr(disk, new_page, &curr_hdr))
+ {
+ fdb->errors |= BATTFS_DISK_WRITE_ERR;
+ return total_write;
+ }
+
+ /* Allocate the missing pages first. */
+ pgoff_t missing_pages = fd->seek_pos / disk->data_size - fdb->max_off;