FAT: add 'errors' mount option

On severe errors FAT remounts itself in read-only mode. Allow to
specify FAT fs desired behavior through 'errors' mount option:
panic, continue or remount read-only.

`mount -t [fat|vfat] -o errors=[panic,remount-ro,continue] \
	<bdev> <mount point>`

This is analog to ext2 fs 'errors' mount option.

Signed-off-by: Denis Karpov <ext-denis.2.karpov@nokia.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Documentation/filesystems/vfat.txt

@@ -132,6 +132,11 @@ rodir	      -- FAT has the ATTR_RO (read-only) attribute. But on Windows,
 		 If you want to use ATTR_RO as read-only flag even for
 		 the directory, set this option.
 
+errors=panic|continue|remount-ro
+	      -- specify FAT behavior on critical errors: panic, continue
+		 without doing anything or remount the partition in
+		 read-only mode (default behavior).
+
 <bool>: 0,1,yes,no,true,false
 
 TODO

fs/fat/cache.c

@@ -241,7 +241,7 @@ int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 	while (*fclus < cluster) {
 		/* prevent the infinite loop of cluster chain */
 		if (*fclus > limit) {
-			fat_fs_panic(sb, "%s: detected the cluster chain loop"
+			fat_fs_error(sb, "%s: detected the cluster chain loop"
 				     " (i_pos %lld)", __func__,
 				     MSDOS_I(inode)->i_pos);
 			nr = -EIO;
@@ -252,7 +252,7 @@ int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 		if (nr < 0)
 			goto out;
 		else if (nr == FAT_ENT_FREE) {
-			fat_fs_panic(sb, "%s: invalid cluster chain"
+			fat_fs_error(sb, "%s: invalid cluster chain"
 				     " (i_pos %lld)", __func__,
 				     MSDOS_I(inode)->i_pos);
 			nr = -EIO;
@@ -285,7 +285,7 @@ static int fat_bmap_cluster(struct inode *inode, int cluster)
 	if (ret < 0)
 		return ret;
 	else if (ret == FAT_ENT_EOF) {
-		fat_fs_panic(sb, "%s: request beyond EOF (i_pos %lld)",
+		fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",
 			     __func__, MSDOS_I(inode)->i_pos);
 		return -EIO;
 	}

fs/fat/dir.c

@@ -1334,7 +1334,7 @@ found:
 			goto error_remove;
 		}
 		if (dir->i_size & (sbi->cluster_size - 1)) {
-			fat_fs_panic(sb, "Odd directory size");
+			fat_fs_error(sb, "Odd directory size");
 			dir->i_size = (dir->i_size + sbi->cluster_size - 1)
 				& ~((loff_t)sbi->cluster_size - 1);
 		}

fs/fat/fat.h

@@ -17,6 +17,10 @@
 #define VFAT_SFN_CREATE_WIN95	0x0100 /* emulate win95 rule for create */
 #define VFAT_SFN_CREATE_WINNT	0x0200 /* emulate winnt rule for create */
 
+#define FAT_ERRORS_CONT		1      /* ignore error and continue */
+#define FAT_ERRORS_PANIC	2      /* panic on error */
+#define FAT_ERRORS_RO		3      /* remount r/o on error */
+
 struct fat_mount_options {
 	uid_t fs_uid;
 	gid_t fs_gid;
@@ -26,6 +30,7 @@ struct fat_mount_options {
 	char *iocharset;          /* Charset used for filename input/display */
 	unsigned short shortname; /* flags for shortname display/create rule */
 	unsigned char name_check; /* r = relaxed, n = normal, s = strict */
+	unsigned char errors;	  /* On error: continue, panic, remount-ro */
 	unsigned short allow_utime;/* permission for setting the [am]time */
 	unsigned quiet:1,         /* set = fake successful chmods and chowns */
 		 showexec:1,      /* set = only set x bit for com/exe/bat */
@@ -310,7 +315,7 @@ extern int fat_fill_super(struct super_block *sb, void *data, int silent,
 extern int fat_flush_inodes(struct super_block *sb, struct inode *i1,
 		            struct inode *i2);
 /* fat/misc.c */
-extern void fat_fs_panic(struct super_block *s, const char *fmt, ...)
+extern void fat_fs_error(struct super_block *s, const char *fmt, ...)
 	__attribute__ ((format (printf, 2, 3))) __cold;
 extern void fat_clusters_flush(struct super_block *sb);
 extern int fat_chain_add(struct inode *inode, int new_dclus, int nr_cluster);

fs/fat/fatent.c

@@ -345,7 +345,7 @@ int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
 
 	if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
 		fatent_brelse(fatent);
-		fat_fs_panic(sb, "invalid access to FAT (entry 0x%08x)", entry);
+		fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
 		return -EIO;
 	}
 
@@ -557,7 +557,7 @@ int fat_free_clusters(struct inode *inode, int cluster)
 			err = cluster;
 			goto error;
 		} else if (cluster == FAT_ENT_FREE) {
-			fat_fs_panic(sb, "%s: deleting FAT entry beyond EOF",
+			fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
 				     __func__);
 			err = -EIO;
 			goto error;

fs/fat/file.c

@@ -213,7 +213,7 @@ static int fat_free(struct inode *inode, int skip)
 			fatent_brelse(&fatent);
 			return 0;
 		} else if (ret == FAT_ENT_FREE) {
-			fat_fs_panic(sb,
+			fat_fs_error(sb,
 				     "%s: invalid cluster chain (i_pos %lld)",
 				     __func__, MSDOS_I(inode)->i_pos);
 			ret = -EIO;

fs/fat/inode.c

@@ -76,7 +76,7 @@ static inline int __fat_get_block(struct inode *inode, sector_t iblock,
 		return 0;
 
 	if (iblock != MSDOS_I(inode)->mmu_private >> sb->s_blocksize_bits) {
-		fat_fs_panic(sb, "corrupted file size (i_pos %lld, %lld)",
+		fat_fs_error(sb, "corrupted file size (i_pos %lld, %lld)",
 			MSDOS_I(inode)->i_pos, MSDOS_I(inode)->mmu_private);
 		return -EIO;
 	}
@@ -834,6 +834,12 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
 		seq_puts(m, ",flush");
 	if (opts->tz_utc)
 		seq_puts(m, ",tz=UTC");
+	if (opts->errors == FAT_ERRORS_CONT)
+		seq_puts(m, ",errors=continue");
+	else if (opts->errors == FAT_ERRORS_PANIC)
+		seq_puts(m, ",errors=panic");
+	else
+		seq_puts(m, ",errors=remount-ro");
 
 	return 0;
 }
@@ -846,7 +852,8 @@ enum {
 	Opt_charset, Opt_shortname_lower, Opt_shortname_win95,
 	Opt_shortname_winnt, Opt_shortname_mixed, Opt_utf8_no, Opt_utf8_yes,
 	Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
-	Opt_obsolate, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err,
+	Opt_obsolate, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
+	Opt_err_panic, Opt_err_ro, Opt_err,
 };
 
 static const match_table_t fat_tokens = {
@@ -869,6 +876,11 @@ static const match_table_t fat_tokens = {
 	{Opt_showexec, "showexec"},
 	{Opt_debug, "debug"},
 	{Opt_immutable, "sys_immutable"},
+	{Opt_flush, "flush"},
+	{Opt_tz_utc, "tz=UTC"},
+	{Opt_err_cont, "errors=continue"},
+	{Opt_err_panic, "errors=panic"},
+	{Opt_err_ro, "errors=remount-ro"},
 	{Opt_obsolate, "conv=binary"},
 	{Opt_obsolate, "conv=text"},
 	{Opt_obsolate, "conv=auto"},
@@ -880,8 +892,6 @@ static const match_table_t fat_tokens = {
 	{Opt_obsolate, "cvf_format=%20s"},
 	{Opt_obsolate, "cvf_options=%100s"},
 	{Opt_obsolate, "posix"},
-	{Opt_flush, "flush"},
-	{Opt_tz_utc, "tz=UTC"},
 	{Opt_err, NULL},
 };
 static const match_table_t msdos_tokens = {
@@ -951,6 +961,7 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
 	opts->numtail = 1;
 	opts->usefree = opts->nocase = 0;
 	opts->tz_utc = 0;
+	opts->errors = FAT_ERRORS_RO;
 	*debug = 0;
 
 	if (!options)
@@ -1043,6 +1054,15 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
 		case Opt_tz_utc:
 			opts->tz_utc = 1;
 			break;
+		case Opt_err_cont:
+			opts->errors = FAT_ERRORS_CONT;
+			break;
+		case Opt_err_panic:
+			opts->errors = FAT_ERRORS_PANIC;
+			break;
+		case Opt_err_ro:
+			opts->errors = FAT_ERRORS_RO;
+			break;
 
 		/* msdos specific */
 		case Opt_dots:

fs/fat/misc.c

@@ -12,14 +12,19 @@
 #include "fat.h"
 
 /*
- * fat_fs_panic reports a severe file system problem and sets the file system
- * read-only. The file system can be made writable again by remounting it.
+ * fat_fs_error reports a file system problem that might indicate fa data
+ * corruption/inconsistency. Depending on 'errors' mount option the
+ * panic() is called, or error message is printed FAT and nothing is done,
+ * or filesystem is remounted read-only (default behavior).
+ * In case the file system is remounted read-only, it can be made writable
+ * again by remounting it.
  */
-void fat_fs_panic(struct super_block *s, const char *fmt, ...)
+void fat_fs_error(struct super_block *s, const char *fmt, ...)
 {
+	struct fat_mount_options *opts = &MSDOS_SB(s)->options;
 	va_list args;
 
-	printk(KERN_ERR "FAT: Filesystem panic (dev %s)\n", s->s_id);
+	printk(KERN_ERR "FAT: Filesystem error (dev %s)\n", s->s_id);
 
 	printk(KERN_ERR "    ");
 	va_start(args, fmt);
@@ -27,13 +32,14 @@ void fat_fs_panic(struct super_block *s, const char *fmt, ...)
 	va_end(args);
 	printk("\n");
 
-	if (!(s->s_flags & MS_RDONLY)) {
+	if (opts->errors == FAT_ERRORS_PANIC)
+		panic("    FAT fs panic from previous error\n");
+	else if (opts->errors == FAT_ERRORS_RO && !(s->s_flags & MS_RDONLY)) {
 		s->s_flags |= MS_RDONLY;
 		printk(KERN_ERR "    File system has been set read-only\n");
 	}
 }
-
-EXPORT_SYMBOL_GPL(fat_fs_panic);
+EXPORT_SYMBOL_GPL(fat_fs_error);
 
 /* Flushes the number of free clusters on FAT32 */
 /* XXX: Need to write one per FSINFO block.  Currently only writes 1 */
@@ -124,7 +130,7 @@ int fat_chain_add(struct inode *inode, int new_dclus, int nr_cluster)
 			mark_inode_dirty(inode);
 	}
 	if (new_fclus != (inode->i_blocks >> (sbi->cluster_bits - 9))) {
-		fat_fs_panic(sb, "clusters badly computed (%d != %llu)",
+		fat_fs_error(sb, "clusters badly computed (%d != %llu)",
 			     new_fclus,
 			     (llu)(inode->i_blocks >> (sbi->cluster_bits - 9)));
 		fat_cache_inval_inode(inode);

fs/fat/namei_msdos.c

@@ -608,7 +608,7 @@ error_inode:
 		sinfo.bh = NULL;
 	}
 	if (corrupt < 0) {
-		fat_fs_panic(new_dir->i_sb,
+		fat_fs_error(new_dir->i_sb,
 			     "%s: Filesystem corrupted (i_pos %lld)",
 			     __func__, sinfo.i_pos);
 	}

fs/fat/namei_vfat.c

@@ -1030,7 +1030,7 @@ error_inode:
 		sinfo.bh = NULL;
 	}
 	if (corrupt < 0) {
-		fat_fs_panic(new_dir->i_sb,
+		fat_fs_error(new_dir->i_sb,
 			     "%s: Filesystem corrupted (i_pos %lld)",
 			     __func__, sinfo.i_pos);
 	}