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[PATCH] r/o bind mounts: honor mount writer counts at remount
Originally from: Herbert Poetzl <herbert@13thfloor.at> This is the core of the read-only bind mount patch set. Note that this does _not_ add a "ro" option directly to the bind mount operation. If you require such a mount, you must first do the bind, then follow it up with a 'mount -o remount,ro' operation: If you wish to have a r/o bind mount of /foo on bar: mount --bind /foo /bar mount -o remount,ro /bar Acked-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Christoph Hellwig <hch@infradead.org> Signed-off-by: Dave Hansen <haveblue@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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@ -105,7 +105,11 @@ struct vfsmount *alloc_vfsmnt(const char *name)
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*/
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int __mnt_is_readonly(struct vfsmount *mnt)
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{
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return (mnt->mnt_sb->s_flags & MS_RDONLY);
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if (mnt->mnt_flags & MNT_READONLY)
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return 1;
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if (mnt->mnt_sb->s_flags & MS_RDONLY)
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return 1;
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return 0;
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}
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EXPORT_SYMBOL_GPL(__mnt_is_readonly);
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@ -305,7 +309,7 @@ void mnt_drop_write(struct vfsmount *mnt)
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}
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EXPORT_SYMBOL_GPL(mnt_drop_write);
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int mnt_make_readonly(struct vfsmount *mnt)
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static int mnt_make_readonly(struct vfsmount *mnt)
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{
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int ret = 0;
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@ -318,15 +322,25 @@ int mnt_make_readonly(struct vfsmount *mnt)
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goto out;
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}
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/*
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* actually set mount's r/o flag here to make
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* __mnt_is_readonly() true, which keeps anyone
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* from doing a successful mnt_want_write().
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* nobody can do a successful mnt_want_write() with all
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* of the counts in MNT_DENIED_WRITE and the locks held.
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*/
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spin_lock(&vfsmount_lock);
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if (!ret)
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mnt->mnt_flags |= MNT_READONLY;
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spin_unlock(&vfsmount_lock);
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out:
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unlock_mnt_writers();
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return ret;
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}
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static void __mnt_unmake_readonly(struct vfsmount *mnt)
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{
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spin_lock(&vfsmount_lock);
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mnt->mnt_flags &= ~MNT_READONLY;
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spin_unlock(&vfsmount_lock);
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}
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int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
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{
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mnt->mnt_sb = sb;
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@ -693,7 +707,7 @@ static int show_vfsmnt(struct seq_file *m, void *v)
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seq_putc(m, '.');
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mangle(m, mnt->mnt_sb->s_subtype);
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}
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seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
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seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
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for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
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if (mnt->mnt_sb->s_flags & fs_infop->flag)
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seq_puts(m, fs_infop->str);
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@ -1295,6 +1309,23 @@ static noinline int do_loopback(struct nameidata *nd, char *old_name,
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return err;
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}
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static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
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{
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int error = 0;
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int readonly_request = 0;
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if (ms_flags & MS_RDONLY)
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readonly_request = 1;
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if (readonly_request == __mnt_is_readonly(mnt))
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return 0;
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if (readonly_request)
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error = mnt_make_readonly(mnt);
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else
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__mnt_unmake_readonly(mnt);
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return error;
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}
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/*
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* change filesystem flags. dir should be a physical root of filesystem.
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* If you've mounted a non-root directory somewhere and want to do remount
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@ -1317,7 +1348,10 @@ static noinline int do_remount(struct nameidata *nd, int flags, int mnt_flags,
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return -EINVAL;
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down_write(&sb->s_umount);
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err = do_remount_sb(sb, flags, data, 0);
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if (flags & MS_BIND)
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err = change_mount_flags(nd->path.mnt, flags);
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else
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err = do_remount_sb(sb, flags, data, 0);
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if (!err)
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nd->path.mnt->mnt_flags = mnt_flags;
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up_write(&sb->s_umount);
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@ -1701,6 +1735,8 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
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mnt_flags |= MNT_NODIRATIME;
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if (flags & MS_RELATIME)
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mnt_flags |= MNT_RELATIME;
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if (flags & MS_RDONLY)
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mnt_flags |= MNT_READONLY;
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flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
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MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);
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@ -29,6 +29,7 @@ struct mnt_namespace;
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#define MNT_NOATIME 0x08
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#define MNT_NODIRATIME 0x10
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#define MNT_RELATIME 0x20
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#define MNT_READONLY 0x40 /* does the user want this to be r/o? */
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#define MNT_SHRINKABLE 0x100
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#define MNT_IMBALANCED_WRITE_COUNT 0x200 /* just for debugging */
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