[U-Boot] [PATCH 3/7] FAT: Fix redundant sector read

Benoît Thébaudeau benoit.thebaudeau at advansee.com
Fri Jul 20 00:02:00 CEST 2012


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 at advansee.com>
Cc: Wolfgang Denk <wd at denx.de>
---
 .../fs/fat/fat.c                                   |   59 +++++++++++---------
 1 file changed, 33 insertions(+), 26 deletions(-)

diff --git u-boot-66714b1.orig/fs/fat/fat.c u-boot-66714b1/fs/fat/fat.c
index e628cf7..fcce412 100644
--- u-boot-66714b1.orig/fs/fat/fat.c
+++ u-boot-66714b1/fs/fat/fat.c
@@ -777,7 +777,7 @@ do_fat_read (const char *filename, void *buffer, unsigned long maxsize,
 	volume_info volinfo;
 	fsdata datablock;
 	fsdata *mydata = &datablock;
-	dir_entry *dentptr;
+	dir_entry *dentptr = NULL;
 	__u16 prevcksum = 0xffff;
 	char *subname = "";
 	__u32 cursect;
@@ -876,19 +876,21 @@ do_fat_read (const char *filename, void *buffer, unsigned long maxsize,
 	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];
@@ -1030,28 +1032,33 @@ do_fat_read (const char *filename, void *buffer, unsigned long maxsize,
 		 * 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);


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