FAT: Fix redundant sector read

PATCH Superseded Benoît Thébaudeau 2 participants 3 messages Jul 19, 2012 – Sep 2, 2012 VFAT/FAT/msdos filesystem

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Benoît Thébaudeau

author

2012-07-19 22:02 UTC #0 lore raw

PATCH 3/7 FAT: Fix redundant sector read

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 Beno?t Th?baudeau <[email protected]>

Cc Wolfgang Denk <[email protected]>

---
 .../fs/fat/fat.c                                   |   59 +++++++++++---------
 1 file changed, 33 insertions(+), 26 deletions(-)

fs/fat/fat.c +33 ~~-26~~

index e628cf7..fcce412 100644
@@ -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);

Benoît Thébaudeau

author

2012-07-20 13:20 UTC #1 lore raw

PATCH v2 4/8 FAT: Fix redundant sector read

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 Beno?t Th?baudeau <[email protected]>

Cc Wolfgang Denk <[email protected]>

---
Changes for v2:
- Patch renumbering because of the new v2 1/8.
- Possible code style changes due to the new v2 1/8.

 .../fs/fat/fat.c                                   |   59 +++++++++++---------
 1 file changed, 33 insertions(+), 26 deletions(-)

fs/fat/fat.c +33 ~~-26~~

index 48c8844..fbc2d7d 100644
@@ -775,7 +775,7 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
 	volume_info volinfo;
 	fsdata datablock;
 	fsdata *mydata = &datablock;
-	dir_entry *dentptr;
+	dir_entry *dentptr = NULL;
 	__u16 prevcksum = 0xffff;
 	char *subname = "";
 	__u32 cursect;

@@ -874,19 +874,21 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
 	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];

@@ -1028,28 +1030,33 @@ do_fat_read(const char *filename, void *buffer, unsigned long maxsize, int dols)
 		 * 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);

Wolfgang Denk

Applied

2012-09-02 15:16 UTC #2 lore raw

PATCH v2 4/8 FAT: Fix redundant sector read

Dear Beno?t Th?baudeau,

Quoted 6 lines · In message <[email protected]> you…

With the previous code, the remaining prefetched sectors were read again af> ter each sector. With this patch, each sector is read only once, thus making th> e prefetch useful.
Signed-off-by Beno?t Th?baudeau <[email protected]>
Cc Wolfgang Denk <[email protected]>

Quoted 7 lines

---
Changes for v2:
- Patch renumbering because of the new v2 1/8.
- Possible code style changes due to the new v2 1/8.
.../fs/fat/fat.c | 59 +++++++++++-----> ----
 1 file changed, 33 insertions(+), 26 deletions(-)

Applied, thanks.

Best regards,

Wolfgang Denk

Signature · 5 lines

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