From 3c0ed9c3a561ca744b2b76921bb8352ba2340669 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Stefan=20Br=C3=BCns?= Date: Sun, 11 Sep 2016 22:51:40 +0200 Subject: [PATCH] fs/fat: Do not write unmodified fat entries to disk MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Lukasz Majewski --- 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 826bd85286..df9f2b5656 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 961ccd8e24..babe9c8dd0 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 9d053e6fa6..8ec91cda75 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 */ -- 2.25.1