FAT: Fix redundant sector read

With the previous code, the remaining prefetched sectors were read
again after each sector.  With this patch, each sector is read only
once, thus making the prefetch useful.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Wolfgang Denk <wd@denx.de>

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 48c88448a3085f5c7d099a0787629c6f77a0f6d5..fbc2d7de1116df199ccc1130127f67456ea835da 100644 (file)
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -775,7 +775,7 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
        volume_info volinfo;
        fsdata datablock;
        fsdata *mydata = &datablock;
-       dir_entry *dentptr;
+       dir_entry *dentptr = NULL;
        __u16 prevcksum = 0xffff;
        char *subname = "";
        __u32 cursect;
@@ -874,19 +874,21 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
        while (1) {
                int i;
 
-               debug("FAT read sect=%d, clust_size=%d, DIRENTSPERBLOCK=%zd\n",
-                       cursect, mydata->clust_size, DIRENTSPERBLOCK);
+               if (j == 0) {
+                       debug("FAT read sect=%d, clust_size=%d, DIRENTSPERBLOCK=%zd\n",
+                               cursect, mydata->clust_size, DIRENTSPERBLOCK);
 
-               if (disk_read(cursect,
-                               (mydata->fatsize == 32) ?
-                               (mydata->clust_size) :
-                               PREFETCH_BLOCKS,
-                               do_fat_read_block) < 0) {
-                       debug("Error: reading rootdir block\n");
-                       goto exit;
-               }
+                       if (disk_read(cursect,
+                                       (mydata->fatsize == 32) ?
+                                       (mydata->clust_size) :
+                                       PREFETCH_BLOCKS,
+                                       do_fat_read_block) < 0) {
+                               debug("Error: reading rootdir block\n");
+                               goto exit;
+                       }
 
-               dentptr = (dir_entry *) do_fat_read_block;
+                       dentptr = (dir_entry *) do_fat_read_block;
+               }
 
                for (i = 0; i < DIRENTSPERBLOCK; i++) {
                        char s_name[14], l_name[VFAT_MAXLEN_BYTES];
@@ -1028,28 +1030,33 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
                 * completely processed.
                 */
                ++j;
-               int fat32_end = 0;
-               if ((mydata->fatsize == 32) && (j == mydata->clust_size)) {
-                       int nxtsect = 0;
-                       int nxt_clust = 0;
+               int rootdir_end = 0;
+               if (mydata->fatsize == 32) {
+                       if (j == mydata->clust_size) {
+                               int nxtsect = 0;
+                               int nxt_clust = 0;
 
-                       nxt_clust = get_fatent(mydata, root_cluster);
-                       fat32_end = CHECK_CLUST(nxt_clust, 32);
+                               nxt_clust = get_fatent(mydata, root_cluster);
+                               rootdir_end = CHECK_CLUST(nxt_clust, 32);
 
-                       nxtsect = mydata->data_begin +
-                               (nxt_clust * mydata->clust_size);
+                               nxtsect = mydata->data_begin +
+                                       (nxt_clust * mydata->clust_size);
 
-                       root_cluster = nxt_clust;
+                               root_cluster = nxt_clust;
 
-                       cursect = nxtsect;
-                       j = 0;
+                               cursect = nxtsect;
+                               j = 0;
+                       }
                } else {
-                       cursect++;
+                       if (j == PREFETCH_BLOCKS)
+                               j = 0;
+
+                       rootdir_end = (++cursect - mydata->rootdir_sect >=
+                                      rootdir_size);
                }
 
                /* If end of rootdir reached */
-               if ((mydata->fatsize == 32 && fat32_end) ||
-                   (mydata->fatsize != 32 && j == rootdir_size)) {
+               if (rootdir_end) {
                        if (dols == LS_ROOT) {
                                printf("\n%d file(s), %d dir(s)\n\n",
                                       files, dirs);