[U-Boot] [PATCH v3] fs: fat: read: fix fat16 ls/read issue

[Przemyslaw Marczak]

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 at samsung.com>
Cc: Mikhail Zolotaryov <lebon at lebon.org.ua>
Cc: Tom Rini <trini at ti.com>
Cc: Stephen Warren <swarren at nvidia.com>
Cc: Simon Glass <sjg at chromium.org>
Cc: Suriyan Ramasami <suriyan.r at gmail.com>
Cc: Lukasz Majewski <l.majewski at samsung.com>
Cc: Wolfgang Denk <wd at denx.de>
Tested-by: Simon Glass <sjg at chomium.org>

---
Changes v2:
- add more expressive variable names
- add code comment to the patch change

Changes v3:
- add Tested-by
---
 fs/fat/fat.c | 69 ++++++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 51 insertions(+), 18 deletions(-)

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 04a51db..bccc3e3 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -823,8 +823,11 @@ int do_fat_read_at(const char *filename, loff_t pos, void *buffer,
 	int 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");
@@ -909,24 +912,54 @@ int do_fat_read_at(const char *filename, loff_t 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++) {
@@ -951,7 +984,7 @@ int do_fat_read_at(const char *filename, loff_t pos, void *buffer,
 
 					get_vfatname(mydata,
 						     root_cluster,
-						     do_fat_read_at_block,
+						     dir_ptr,
 						     dentptr, l_name);
 
 					if (dols == LS_ROOT) {
@@ -1062,7 +1095,7 @@ int do_fat_read_at(const char *filename, loff_t 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);
 
 		/*
@@ -1070,10 +1103,10 @@ int do_fat_read_at(const char *filename, loff_t 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;
 
@@ -1086,11 +1119,11 @@ int do_fat_read_at(const char *filename, loff_t 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);
-- 
1.9.1