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>

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 826bd852860aed9a078a75ad618f5d204cdef9f1..df9f2b56562aafae900974fb85ac236d3d8a2975 100644 (file)
--- 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 961ccd8e24643e6f626551de0e3356e8a4489957..babe9c8dd025eff59f9ee226d278ec000662c883 100644 (file)
--- 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 9d053e6fa67e31c8c6f10276508c1d6f4e37b1ab..8ec91cda753ba562d9877a1d76a983b17150b5d3 100644 (file)
--- 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 */