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-rw-r--r--fs/fat/fat.c69
1 files changed, 51 insertions, 18 deletions
diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 04a51db6d4..bccc3e3ed8 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);
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