[U-Boot] [PATCH 2/4] fs/fat: Do not write unmodified fat entries to disk

[Lukasz Majewski]

Hi Stefan,

> 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 at rwth-aachen.de>
> ---
>  fs/fat/fat.c       |  1 +
>  fs/fat/fat_write.c | 31 +++++++++++++++++++------------
>  include/fat.h      |  1 +
>  3 files changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/fat/fat.c b/fs/fat/fat.c
> index 826bd85..df9f2b5 100644
> --- a/fs/fat/fat.c
> +++ b/fs/fat/fat.c
> @@ -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");
> diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
> index 961ccd8..babe9c8 100644
> --- a/fs/fat/fat_write.c
> +++ b/fs/fat/fat_write.c
> @@ -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;
> diff --git a/include/fat.h b/include/fat.h
> index 9d053e6..8ec91cd 100644
> --- a/include/fat.h
> +++ b/include/fat.h
> @@ -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 */

Reviewed-by: Lukasz Majewski <l.majewski at samsung.com>

-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group