fat: Fix ATTR_RO for directory

FAT has the ATTR_RO (read-only) attribute. But on Windows, the ATTR_RO
of the directory will be just ignored actually, and is used by only
applications as flag. E.g. it's setted for the customized folder by
Explorer.

http://msdn2.microsoft.com/en-us/library/aa969337.aspx

This adds "rodir" option. If user specified it, ATTR_RO is used as
read-only flag even if it's the directory. Otherwise, inode->i_mode
is not used to hold ATTR_RO (i.e. fat_mode_can_save_ro() returns 0).

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>

4 files changed, 43 insertions, 12 deletions

diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
index dc9dc73d7d38..3a5ddc96901a 100644
--- a/Documentation/filesystems/vfat.txt
+++ b/Documentation/filesystems/vfat.txt
@@ -124,6 +124,14 @@ sys_immutable -- If set, ATTR_SYS attribute on FAT is handled as
 flush         -- If set, the filesystem will try to flush to disk more
                  early than normal. Not set by default.
 
+rodir         -- FAT has the ATTR_RO (read-only) attribute. But on Windows,
+                 the ATTR_RO of the directory will be just ignored actually,
+                 and is used by only applications as flag. E.g. it's setted
+                 for the customized folder.
+
+                 If you want to use ATTR_RO as read-only flag even for
+                 the directory, set this option.
+
 <bool>: 0,1,yes,no,true,false
 
 TODO
diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 313b645b8126..e9dce5d8e7a7 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -38,7 +38,8 @@ struct fat_mount_options {
                  flush:1,         /* write things quickly */
                  nocase:1,        /* Does this need case conversion? 0=need case conversion*/
                  usefree:1,       /* Use free_clusters for FAT32 */
-                 tz_utc:1;        /* Filesystem timestamps are in UTC */
+                 tz_utc:1,        /* Filesystem timestamps are in UTC */
+                 rodir:1;         /* allow ATTR_RO for directory */
 };
 
 #define FAT_HASH_BITS   8
@@ -120,15 +121,20 @@ static inline struct msdos_inode_info *MSDOS_I(struct inode *inode)
 /*
  * If ->i_mode can't hold S_IWUGO (i.e. ATTR_RO), we use ->i_attrs to
  * save ATTR_RO instead of ->i_mode.
+ *
+ * If it's directory and !sbi->options.rodir, ATTR_RO isn't read-only
+ * bit, it's just used as flag for app.
  */
 static inline int fat_mode_can_hold_ro(struct inode *inode)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
         mode_t mask;
 
-        if (S_ISDIR(inode->i_mode))
+        if (S_ISDIR(inode->i_mode)) {
+                if (!sbi->options.rodir)
+                        return 0;
                 mask = ~sbi->options.fs_dmask;
-        else
+        } else
                 mask = ~sbi->options.fs_fmask;
 
         if (!(mask & S_IWUGO))
@@ -140,7 +146,7 @@ static inline int fat_mode_can_hold_ro(struct inode *inode)
 static inline mode_t fat_make_mode(struct msdos_sb_info *sbi,
                                    u8 attrs, mode_t mode)
 {
-        if (attrs & ATTR_RO)
+        if (attrs & ATTR_RO && !((attrs & ATTR_DIR) && !sbi->options.rodir))
                 mode &= ~S_IWUGO;
 
         if (attrs & ATTR_DIR)
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 81b15c623803..f06a4e525ece 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -282,11 +282,18 @@ static int fat_sanitize_mode(const struct msdos_sb_info *sbi,
         /*
          * Of the r and x bits, all (subject to umask) must be present. Of the
          * w bits, either all (subject to umask) or none must be present.
+         *
+         * If fat_mode_can_hold_ro(inode) is false, can't change w bits.
          */
         if ((perm & (S_IRUGO | S_IXUGO)) != (inode->i_mode & (S_IRUGO|S_IXUGO)))
                 return -EPERM;
-        if ((perm & S_IWUGO) && ((perm & S_IWUGO) != (S_IWUGO & ~mask)))
-                return -EPERM;
+        if (fat_mode_can_hold_ro(inode)) {
+                if ((perm & S_IWUGO) && ((perm & S_IWUGO) != (S_IWUGO & ~mask)))
+                        return -EPERM;
+        } else {
+                if ((perm & S_IWUGO) != (S_IWUGO & ~mask))
+                        return -EPERM;
+        }
 
         *mode_ptr &= S_IFMT | perm;
 
@@ -316,8 +323,8 @@ int fat_setattr(struct dentry *dentry, struct iattr *attr)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
         struct inode *inode = dentry->d_inode;
-        int error = 0;
         unsigned int ia_valid;
+        int error;
 
         /*
          * Expand the file. Since inode_setattr() updates ->i_size
@@ -371,7 +378,8 @@ int fat_setattr(struct dentry *dentry, struct iattr *attr)
                         attr->ia_valid &= ~ATTR_MODE;
         }
 
-        error = inode_setattr(inode, attr);
+        if (attr->ia_valid)
+                error = inode_setattr(inode, attr);
 out:
         return error;
 }
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 7aaa21cf019a..0da04e6d1e34 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -797,8 +797,10 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
                         seq_puts(m, ",uni_xlate");
                 if (!opts->numtail)
                         seq_puts(m, ",nonumtail");
+                if (opts->rodir)
+                        seq_puts(m, ",rodir");
         }
-        if (sbi->options.flush)
+        if (opts->flush)
                 seq_puts(m, ",flush");
         if (opts->tz_utc)
                 seq_puts(m, ",tz=UTC");
@@ -814,7 +816,7 @@ 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_err,
+        Opt_obsolate, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err,
 };
 
 static const match_table_t fat_tokens = {
@@ -886,6 +888,7 @@ static const match_table_t vfat_tokens = {
         {Opt_nonumtail_yes, "nonumtail=yes"},
         {Opt_nonumtail_yes, "nonumtail=true"},
         {Opt_nonumtail_yes, "nonumtail"},
+        {Opt_rodir, "rodir"},
         {Opt_err, NULL}
 };
 
@@ -905,10 +908,13 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
         opts->allow_utime = -1;
         opts->codepage = fat_default_codepage;
         opts->iocharset = fat_default_iocharset;
-        if (is_vfat)
+        if (is_vfat) {
                 opts->shortname = VFAT_SFN_DISPLAY_LOWER|VFAT_SFN_CREATE_WIN95;
-        else
+                opts->rodir = 0;
+        } else {
                 opts->shortname = 0;
+                opts->rodir = 1;
+        }
         opts->name_check = 'n';
         opts->quiet = opts->showexec = opts->sys_immutable = opts->dotsOK =  0;
         opts->utf8 = opts->unicode_xlate = 0;
@@ -1059,6 +1065,9 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
                 case Opt_nonumtail_yes:         /* empty or 1 or yes or true */
                         opts->numtail = 0;      /* negated option */
                         break;
+                case Opt_rodir:
+                        opts->rodir = 1;
+                        break;
 
                 /* obsolete mount options */
                 case Opt_obsolate: