fs: fat: read: fix fat16 ls/read issue

The present fat implementation ignores FAT16 long name
directory entries which aren't placed in a single sector.

This was becouse of the buffer was always filled by the
two sectors, and the loop was made also for two sectors.

If some file long name entries are stored in two sectors,
the we have two cases:

Case 1:
Both of sectors are in the buffer - all required data
for long file name is in the buffer.
- Read OK!

Case 2:
The current directory entry is placed at the end of the
second buffered sector. And the next entries are placed
in a sector which is not buffered yet. Then two next
sectors are buffered and the mentioned entry is ignored.
- Read fail!

This commit fixes this issue by:
- read two sectors after loop on each single is done
- keep the last used sector as a first in the buffer
  before the read of two next

The commit doesn't affects the fat32 imlementation,
which works good as previous.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Mikhail Zolotaryov <lebon@lebon.org.ua>
Cc: Tom Rini <trini@ti.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Suriyan Ramasami <suriyan.r@gmail.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Wolfgang Denk <wd@denx.de>
Tested-by: Simon Glass <sjg@chomium.org>
(cherry picked from commit 64f65e1e36adffc39730635d104399937ea21949)

1 files changed, 51 insertions, 18 deletions

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 54f42ea..b2a0828 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -824,8 +824,11 @@ do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
 	long ret = -1;
 	int firsttime;
 	__u32 root_cluster = 0;
+	__u32 read_blk;
 	int rootdir_size = 0;
-	int j;
+	int buffer_blk_cnt;
+	int do_read;
+	__u8 *dir_ptr;
 
 	if (read_bootsectandvi(&bs, &volinfo, &mydata->fatsize)) {
 		debug("Error: reading boot sector\n");
@@ -910,24 +913,54 @@ do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
 		isdir = 1;
 	}
 
-	j = 0;
+	buffer_blk_cnt = 0;
+	firsttime = 1;
 	while (1) {
 		int i;
 
-		if (j == 0) {
-			debug("FAT read sect=%d, clust_size=%d, DIRENTSPERBLOCK=%zd\n",
-				cursect, mydata->clust_size, DIRENTSPERBLOCK);
+		if (mydata->fatsize == 32 || firsttime) {
+			dir_ptr = do_fat_read_at_block;
+			firsttime = 0;
+		} else {
+			/**
+			 * FAT16 sector buffer modification:
+			 * Each loop, the second buffered block is moved to
+			 * the buffer begin, and two next sectors are read
+			 * next to the previously moved one. So the sector
+			 * buffer keeps always 3 sectors for fat16.
+			 * And the current sector is the buffer second sector
+			 * beside the "firsttime" read, when it is the first one.
+			 *
+			 * PREFETCH_BLOCKS is 2 for FAT16 == loop[0:1]
+			 * n = computed root dir sector
+			 * loop |  cursect-1  | cursect    | cursect+1  |
+			 *   0  |  sector n+0 | sector n+1 | none       |
+			 *   1  |  none       | sector n+0 | sector n+1 |
+			 *   0  |  sector n+1 | sector n+2 | sector n+3 |
+			 *   1  |  sector n+3 | ...
+			*/
+			dir_ptr = (do_fat_read_at_block + mydata->sect_size);
+			memcpy(do_fat_read_at_block, dir_ptr, mydata->sect_size);
+		}
+
+		do_read = 1;
+
+		if (mydata->fatsize == 32 && buffer_blk_cnt)
+			do_read = 0;
+
+		if (do_read) {
+			read_blk = (mydata->fatsize == 32) ?
+				    mydata->clust_size : PREFETCH_BLOCKS;
+
+			debug("FAT read(sect=%d, cnt:%d), clust_size=%d, DIRENTSPERBLOCK=%zd\n",
+				cursect, read_blk, mydata->clust_size, DIRENTSPERBLOCK);
 
-			if (disk_read(cursect,
-					(mydata->fatsize == 32) ?
-					(mydata->clust_size) :
-					PREFETCH_BLOCKS,
-					do_fat_read_at_block) < 0) {
+			if (disk_read(cursect, read_blk, dir_ptr) < 0) {
 				debug("Error: reading rootdir block\n");
 				goto exit;
 			}
 
-			dentptr = (dir_entry *) do_fat_read_at_block;
+			dentptr = (dir_entry *)dir_ptr;
 		}
 
 		for (i = 0; i < DIRENTSPERBLOCK; i++) {
@@ -952,7 +985,7 @@ do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
 
 					get_vfatname(mydata,
 						     root_cluster,
-						     do_fat_read_at_block,
+						     dir_ptr,
 						     dentptr, l_name);
 
 					if (dols == LS_ROOT) {
@@ -1063,7 +1096,7 @@ do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
 
 			goto rootdir_done;	/* We got a match */
 		}
-		debug("END LOOP: j=%d   clust_size=%d\n", j,
+		debug("END LOOP: buffer_blk_cnt=%d   clust_size=%d\n", buffer_blk_cnt,
 		       mydata->clust_size);
 
 		/*
@@ -1071,10 +1104,10 @@ do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
 		 * root directory clusters when a cluster has been
 		 * completely processed.
 		 */
-		++j;
+		++buffer_blk_cnt;
 		int rootdir_end = 0;
 		if (mydata->fatsize == 32) {
-			if (j == mydata->clust_size) {
+			if (buffer_blk_cnt == mydata->clust_size) {
 				int nxtsect = 0;
 				int nxt_clust = 0;
 
@@ -1087,11 +1120,11 @@ do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
 				root_cluster = nxt_clust;
 
 				cursect = nxtsect;
-				j = 0;
+				buffer_blk_cnt = 0;
 			}
 		} else {
-			if (j == PREFETCH_BLOCKS)
-				j = 0;
+			if (buffer_blk_cnt == PREFETCH_BLOCKS)
+				buffer_blk_cnt = 0;
 
 			rootdir_end = (++cursect - mydata->rootdir_sect >=
 				       rootdir_size);