fat: Update free_clusters even if it is untrusted

Currently, free_clusters is not updated until it is trusted, because
Windows doesn't update it correctly.

But if user is using FAT driver of Linux, it updates free_clusters
correctly.  Instead, this updates it even if it's untrusted, so if
free_clustes is correct, now keep correct value.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 10 insertions, 5 deletions

diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index 5fb366992b73..c7c8ab2209e1 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -450,7 +450,8 @@ int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
         BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));    /* fixed limit */
 
         lock_fat(sbi);
-        if (sbi->free_clusters != -1 && sbi->free_clusters < nr_cluster) {
+        if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
+            sbi->free_clusters < nr_cluster) {
                 unlock_fat(sbi);
                 return -ENOSPC;
         }
@@ -504,6 +505,7 @@ int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
 
         /* Couldn't allocate the free entries */
         sbi->free_clusters = 0;
+        sbi->free_clus_valid = 1;
         sb->s_dirt = 1;
         err = -ENOSPC;
 
@@ -615,7 +617,7 @@ int fat_count_free_clusters(struct super_block *sb)
         int err = 0, free;
 
         lock_fat(sbi);
-        if (sbi->free_clusters != -1)
+        if (sbi->free_clusters != -1 && sbi->free_clus_valid)
                 goto out;
 
         reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
@@ -643,6 +645,7 @@ int fat_count_free_clusters(struct super_block *sb)
                 } while (fat_ent_next(sbi, &fatent));
         }
         sbi->free_clusters = free;
+        sbi->free_clus_valid = 1;
         sb->s_dirt = 1;
         fatent_brelse(&fatent);
 out:
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 886f6095a378..1604a8a5c01f 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -537,7 +537,7 @@ static int fat_statfs(struct dentry *dentry, struct kstatfs *buf)
         struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
 
         /* If the count of free cluster is still unknown, counts it here. */
-        if (sbi->free_clusters == -1) {
+        if (sbi->free_clusters == -1 || !sbi->free_clus_valid) {
                 int err = fat_count_free_clusters(dentry->d_sb);
                 if (err)
                         return err;
@@ -1274,6 +1274,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
         sbi->fat_length = le16_to_cpu(b->fat_length);
         sbi->root_cluster = 0;
         sbi->free_clusters = -1;        /* Don't know yet */
+        sbi->free_clus_valid = 0;
         sbi->prev_free = FAT_START_ENT;
 
         if (!sbi->fat_length && b->fat32_length) {
@@ -1309,8 +1310,8 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
                                sbi->fsinfo_sector);
                 } else {
                         if (sbi->options.usefree)
-                                sbi->free_clusters =
-                                        le32_to_cpu(fsinfo->free_clusters);
+                                sbi->free_clus_valid = 1;
+                        sbi->free_clusters = le32_to_cpu(fsinfo->free_clusters);
                         sbi->prev_free = le32_to_cpu(fsinfo->next_cluster);
                 }
 
diff --git a/include/linux/msdos_fs.h b/include/linux/msdos_fs.h
index 81fb9bc53220..0bca157ddca5 100644
--- a/include/linux/msdos_fs.h
+++ b/include/linux/msdos_fs.h
@@ -233,6 +233,7 @@ struct msdos_sb_info {
         struct mutex fat_lock;
         unsigned int prev_free;      /* previously allocated cluster number */
         unsigned int free_clusters;  /* -1 if undefined */
+        unsigned int free_clus_valid; /* is free_clusters valid? */
         struct fat_mount_options options;
         struct nls_table *nls_disk;  /* Codepage used on disk */
         struct nls_table *nls_io;    /* Charset used for input and display */