FAT: Make it possible to read from any file position

When storage devices contain files larger than the embedded RAM, it is
useful to be able to read these files by chunks, e.g. for a software
update to the embedded NAND Flash from an external storage device (USB
stick, SD card, etc.).

Hence, this patch makes it possible by adding a new FAT API to read
files from a given position. This patch also adds this feature to the
fatload command.

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

1 files changed, 79 insertions, 19 deletions

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 19f6a8c..41ae15e 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -328,13 +328,16 @@ get_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer, unsigned long size)
 }
 
 /*
- * Read at most 'maxsize' bytes from the file associated with 'dentptr'
+ * Read at most 'maxsize' bytes from 'pos' in the file associated with 'dentptr'
  * into 'buffer'.
  * Return the number of bytes read or -1 on fatal errors.
  */
+__u8 get_contents_vfatname_block[MAX_CLUSTSIZE]
+	__aligned(ARCH_DMA_MINALIGN);
+
 static long
-get_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
-	     unsigned long maxsize)
+get_contents(fsdata *mydata, dir_entry *dentptr, unsigned long pos,
+	     __u8 *buffer, unsigned long maxsize)
 {
 	unsigned long filesize = FAT2CPU32(dentptr->size), gotsize = 0;
 	unsigned int bytesperclust = mydata->clust_size * mydata->sect_size;
@@ -344,12 +347,59 @@ get_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
 
 	debug("Filesize: %ld bytes\n", filesize);
 
-	if (maxsize > 0 && filesize > maxsize)
-		filesize = maxsize;
+	if (pos >= filesize) {
+		debug("Read position past EOF: %lu\n", pos);
+		return gotsize;
+	}
+
+	if (maxsize > 0 && filesize > pos + maxsize)
+		filesize = pos + maxsize;
 
 	debug("%ld bytes\n", filesize);
 
 	actsize = bytesperclust;
+
+	/* go to cluster at pos */
+	while (actsize <= pos) {
+		curclust = get_fatent(mydata, curclust);
+		if (CHECK_CLUST(curclust, mydata->fatsize)) {
+			debug("curclust: 0x%x\n", curclust);
+			debug("Invalid FAT entry\n");
+			return gotsize;
+		}
+		actsize += bytesperclust;
+	}
+
+	/* actsize > pos */
+	actsize -= bytesperclust;
+	filesize -= actsize;
+	pos -= actsize;
+
+	/* align to beginning of next cluster if any */
+	if (pos) {
+		actsize = min(filesize, bytesperclust);
+		if (get_cluster(mydata, curclust, get_contents_vfatname_block,
+				(int)actsize) != 0) {
+			printf("Error reading cluster\n");
+			return -1;
+		}
+		filesize -= actsize;
+		actsize -= pos;
+		memcpy(buffer, get_contents_vfatname_block + pos, actsize);
+		gotsize += actsize;
+		if (!filesize)
+			return gotsize;
+		buffer += actsize;
+
+		curclust = get_fatent(mydata, curclust);
+		if (CHECK_CLUST(curclust, mydata->fatsize)) {
+			debug("curclust: 0x%x\n", curclust);
+			debug("Invalid FAT entry\n");
+			return gotsize;
+		}
+	}
+
+	actsize = bytesperclust;
 	endclust = curclust;
 
 	do {
@@ -433,9 +483,6 @@ static int slot2str(dir_slot *slotptr, char *l_name, int *idx)
  * into 'retdent'
  * Return 0 on success, -1 otherwise.
  */
-__u8 get_vfatname_block[MAX_CLUSTSIZE]
-	__aligned(ARCH_DMA_MINALIGN);
-
 static int
 get_vfatname(fsdata *mydata, int curclust, __u8 *cluster,
 	     dir_entry *retdent, char *l_name)
@@ -474,13 +521,13 @@ get_vfatname(fsdata *mydata, int curclust, __u8 *cluster,
 			return -1;
 		}
 
-		if (get_cluster(mydata, curclust, get_vfatname_block,
+		if (get_cluster(mydata, curclust, get_contents_vfatname_block,
 				mydata->clust_size * mydata->sect_size) != 0) {
 			debug("Error: reading directory block\n");
 			return -1;
 		}
 
-		slotptr2 = (dir_slot *)get_vfatname_block;
+		slotptr2 = (dir_slot *)get_contents_vfatname_block;
 		while (counter > 0) {
 			if (((slotptr2->id & ~LAST_LONG_ENTRY_MASK)
 			    & 0xff) != counter)
@@ -491,7 +538,7 @@ get_vfatname(fsdata *mydata, int curclust, __u8 *cluster,
 
 		/* Save the real directory entry */
 		realdent = (dir_entry *)slotptr2;
-		while ((__u8 *)slotptr2 > get_vfatname_block) {
+		while ((__u8 *)slotptr2 > get_contents_vfatname_block) {
 			slotptr2--;
 			slot2str(slotptr2, l_name, &idx);
 		}
@@ -770,11 +817,12 @@ exit:
 	return ret;
 }
 
-__u8 do_fat_read_block[MAX_CLUSTSIZE]
+__u8 do_fat_read_at_block[MAX_CLUSTSIZE]
 	__aligned(ARCH_DMA_MINALIGN);
 
 long
-do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
+do_fat_read_at(const char *filename, unsigned long pos, void *buffer,
+	       unsigned long maxsize, int dols)
 {
 	char fnamecopy[2048];
 	boot_sector bs;
@@ -888,12 +936,12 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
 					(mydata->fatsize == 32) ?
 					(mydata->clust_size) :
 					PREFETCH_BLOCKS,
-					do_fat_read_block) < 0) {
+					do_fat_read_at_block) < 0) {
 				debug("Error: reading rootdir block\n");
 				goto exit;
 			}
 
-			dentptr = (dir_entry *) do_fat_read_block;
+			dentptr = (dir_entry *) do_fat_read_at_block;
 		}
 
 		for (i = 0; i < DIRENTSPERBLOCK; i++) {
@@ -913,7 +961,7 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
 
 					get_vfatname(mydata,
 						     root_cluster,
-						     do_fat_read_block,
+						     do_fat_read_at_block,
 						     dentptr, l_name);
 
 					if (dols == LS_ROOT) {
@@ -1116,7 +1164,7 @@ rootdir_done:
 			subname = nextname;
 	}
 
-	ret = get_contents(mydata, dentptr, buffer, maxsize);
+	ret = get_contents(mydata, dentptr, pos, buffer, maxsize);
 	debug("Size: %d, got: %ld\n", FAT2CPU32(dentptr->size), ret);
 
 exit:
@@ -1124,6 +1172,12 @@ exit:
 	return ret;
 }
 
+long
+do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
+{
+	return do_fat_read_at(filename, 0, buffer, maxsize, dols);
+}
+
 int file_fat_detectfs(void)
 {
 	boot_sector bs;
@@ -1192,8 +1246,14 @@ int file_fat_ls(const char *dir)
 	return do_fat_read(dir, NULL, 0, LS_YES);
 }
 
-long file_fat_read(const char *filename, void *buffer, unsigned long maxsize)
+long file_fat_read_at(const char *filename, unsigned long pos, void *buffer,
+		      unsigned long maxsize)
 {
 	printf("reading %s\n", filename);
-	return do_fat_read(filename, buffer, maxsize, LS_NO);
+	return do_fat_read_at(filename, pos, buffer, maxsize, LS_NO);
+}
+
+long file_fat_read(const char *filename, void *buffer, unsigned long maxsize)
+{
+	return file_fat_read_at(filename, 0, buffer, maxsize);
 }