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fs/fat: Do not write unmodified fat entries to disk 

The code caches 6 sectors of the FAT. On FAT traversal, the old contents
needs to be flushed to disk, but only if any FAT entries had been modified.
Explicitly flag the buffer on modification.

Currently, creating a new file traverses the whole FAT up to the first
free cluster and rewrites the on-disk blocks.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
This commit is contained in:
Stefan Brüns 2016-09-11 22:51:40 +02:00 committed by Tom Rini
parent ed76f91277
commit 3c0ed9c3a5
3 changed files with 21 additions and 12 deletions
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1
fs/fat/fat.c
View File

@ -876,6 +876,7 @@ int do_fat_read_at(const char *filename, loff_t pos, void *buffer,
}
mydata->fatbufnum = -1;
mydata->fat_dirty = 0;
mydata->fatbuf = memalign(ARCH_DMA_MINALIGN, FATBUFSIZE);
if (mydata->fatbuf == NULL) {
debug("Error: allocating memory\n");

31
fs/fat/fat_write.c
View File

@ -104,13 +104,19 @@ static __u8 num_of_fats;
/*
* Write fat buffer into block device
*/
static int flush_fat_buffer(fsdata *mydata)
static int flush_dirty_fat_buffer(fsdata *mydata)
{
int getsize = FATBUFBLOCKS;
__u32 fatlength = mydata->fatlength;
__u8 *bufptr = mydata->fatbuf;
__u32 startblock = mydata->fatbufnum * FATBUFBLOCKS;
debug("debug: evicting %d, dirty: %d\n", mydata->fatbufnum,
(int)mydata->fat_dirty);
if ((!mydata->fat_dirty) || (mydata->fatbufnum == -1))
return 0;
startblock += mydata->fat_sect;
if (getsize > fatlength)
@ -130,6 +136,7 @@ static int flush_fat_buffer(fsdata *mydata)
return -1;
}
}
mydata->fat_dirty = 0;
return 0;
}
@ -186,10 +193,8 @@ static __u32 get_fatent_value(fsdata *mydata, __u32 entry)
startblock += mydata->fat_sect; /* Offset from start of disk */
/* Write back the fatbuf to the disk */
if (mydata->fatbufnum != -1) {
if (flush_fat_buffer(mydata) < 0)
return -1;
}
if (flush_dirty_fat_buffer(mydata) < 0)
return -1;
if (disk_read(startblock, getsize, bufptr) < 0) {
debug("Error reading FAT blocks\n");
@ -494,10 +499,8 @@ static int set_fatent_value(fsdata *mydata, __u32 entry, __u32 entry_value)
if (getsize > fatlength)
getsize = fatlength;
if (mydata->fatbufnum != -1) {
if (flush_fat_buffer(mydata) < 0)
return -1;
}
if (flush_dirty_fat_buffer(mydata) < 0)
return -1;
if (disk_read(startblock, getsize, bufptr) < 0) {
debug("Error reading FAT blocks\n");
@ -506,6 +509,9 @@ static int set_fatent_value(fsdata *mydata, __u32 entry, __u32 entry_value)
mydata->fatbufnum = bufnum;
}
/* Mark as dirty */
mydata->fat_dirty = 1;
/* Set the actual entry */
switch (mydata->fatsize) {
case 32:
@ -645,7 +651,7 @@ static void flush_dir_table(fsdata *mydata, dir_entry **dentptr)
dir_curclust = dir_newclust;
if (flush_fat_buffer(mydata) < 0)
if (flush_dirty_fat_buffer(mydata) < 0)
return;
memset(get_dentfromdir_block, 0x00,
@ -675,7 +681,7 @@ static int clear_fatent(fsdata *mydata, __u32 entry)
}
/* Flush fat buffer */
if (flush_fat_buffer(mydata) < 0)
if (flush_dirty_fat_buffer(mydata) < 0)
return -1;
return 0;
@ -1011,6 +1017,7 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
}
mydata->fatbufnum = -1;
mydata->fat_dirty = 0;
mydata->fatbuf = memalign(ARCH_DMA_MINALIGN, FATBUFSIZE);
if (mydata->fatbuf == NULL) {
debug("Error: allocating memory\n");
@ -1111,7 +1118,7 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
debug("attempt to write 0x%llx bytes\n", *actwrite);
/* Flush fat buffer */
ret = flush_fat_buffer(mydata);
ret = flush_dirty_fat_buffer(mydata);
if (ret) {
printf("Error: flush fat buffer\n");
goto exit;

1
include/fat.h
View File

@ -169,6 +169,7 @@ typedef struct {
int fatsize; /* Size of FAT in bits */
__u32 fatlength; /* Length of FAT in sectors */
__u16 fat_sect; /* Starting sector of the FAT */
__u8 fat_dirty; /* Set if fatbuf has been modified */
__u32 rootdir_sect; /* Start sector of root directory */
__u16 sect_size; /* Size of sectors in bytes */
__u16 clust_size; /* Size of clusters in sectors */