Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750788AbWHAX7l (ORCPT ); Tue, 1 Aug 2006 19:59:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750762AbWHAXwz (ORCPT ); Tue, 1 Aug 2006 19:52:55 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:10726 "EHLO e2.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1750761AbWHAXws (ORCPT ); Tue, 1 Aug 2006 19:52:48 -0400 Subject: [PATCH 07/28] Add vfsmount writer count To: linux-kernel@vger.kernel.org Cc: viro@ftp.linux.org.uk, herbert@13thfloor.at, hch@infradead.org, Dave Hansen From: Dave Hansen Date: Tue, 01 Aug 2006 16:52:45 -0700 References: <20060801235240.82ADCA42@localhost.localdomain> In-Reply-To: <20060801235240.82ADCA42@localhost.localdomain> Message-Id: <20060801235245.08138ED2@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9488 Lines: 302 This allows a vfsmount to keep track of how many instances of files open for write there are at a given time. A mount can refuse to allow writers. This can be because it is a read-only bind mount, or for other functionality in the future. A mount can also now refuse to make a transition from r/w to r/o whenever it has currently active writers. When a mount gets its first writer, it tells the superblock about it by incrementing sb->s_mnt_writers. When the last writer goes away, this count is bumped back down. This makes the question of whether or not anything is writing to the sb a much quicker, easier operation than scanning the open files list. The WARN_ON()s can go away before this is merged into mainline provided it has had some time in -mm or equivalent. Signed-off-by: Dave Hansen --- lxc-dave/fs/namespace.c | 61 +++++++++++++++++++++++++++++++++++++ lxc-dave/fs/super.c | 66 +++++++++++++++++++++++++++++++++++++---- lxc-dave/include/linux/fs.h | 2 + lxc-dave/include/linux/mount.h | 18 +++++++++++ 4 files changed, 142 insertions(+), 5 deletions(-) diff -puN fs/namespace.c~C-add-vfsmount-writer_count fs/namespace.c --- lxc/fs/namespace.c~C-add-vfsmount-writer_count 2006-08-01 16:35:18.000000000 -0700 +++ lxc-dave/fs/namespace.c 2006-08-01 16:35:19.000000000 -0700 @@ -58,6 +58,7 @@ struct vfsmount *alloc_vfsmnt(const char if (mnt) { memset(mnt, 0, sizeof(struct vfsmount)); atomic_set(&mnt->mnt_count, 1); + atomic_set(&mnt->mnt_writers, 0); INIT_LIST_HEAD(&mnt->mnt_hash); INIT_LIST_HEAD(&mnt->mnt_child); INIT_LIST_HEAD(&mnt->mnt_mounts); @@ -886,6 +887,60 @@ out_unlock: return err; } +int mnt_make_readonly(struct vfsmount *mnt) +{ + int ret = 0; + + WARN_ON(__mnt_is_readonly(mnt)); + + /* + * This flag set is actually redundant with what + * happens in do_remount(), but since we do this + * under the lock, anyone attempting to get a write + * on it after this will fail. + */ + spin_lock(&mnt->mnt_sb->s_mnt_writers_lock); + if (!atomic_read(&mnt->mnt_writers)) + mnt->mnt_flags |= MNT_READONLY; + else + ret = -EBUSY; + spin_unlock(&mnt->mnt_sb->s_mnt_writers_lock); + return ret; +} + +int mnt_want_write(struct vfsmount *mnt) +{ + int ret = 0; +repeat: + if (atomic_add_unless(&mnt->mnt_writers, 1, 0)) + return 0; + + spin_lock(&mnt->mnt_sb->s_mnt_writers_lock); + if (__mnt_is_readonly(mnt)) { + ret = -EROFS; + goto out; + } + if (atomic_add_return(1, &mnt->mnt_writers) != 1) { + atomic_dec(&mnt->mnt_writers); + spin_unlock(&mnt->mnt_sb->s_mnt_writers_lock); + goto repeat; + } + atomic_inc(&mnt->mnt_sb->s_mnt_writers); +out: + spin_unlock(&mnt->mnt_sb->s_mnt_writers_lock); + return ret; +} + +void mnt_drop_write(struct vfsmount *mnt) +{ + if (!atomic_dec_and_lock(&mnt->mnt_writers, + &mnt->mnt_sb->s_mnt_writers_lock)) + return; + + atomic_dec(&mnt->mnt_sb->s_mnt_writers); + spin_unlock(&mnt->mnt_sb->s_mnt_writers_lock); +} + /* * recursively change the type of the mountpoint. */ @@ -977,6 +1032,8 @@ static int do_remount(struct nameidata * down_write(&sb->s_umount); err = do_remount_sb(sb, flags, data, 0); + if (!(sb->s_flags & MS_RDONLY)) + mnt_flags |= MNT_SB_WRITABLE; if (!err) nd->mnt->mnt_flags = mnt_flags; up_write(&sb->s_umount); @@ -1117,6 +1174,8 @@ int do_add_mount(struct vfsmount *newmnt if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode)) goto unlock; + if (!(newmnt->mnt_sb->s_flags & MS_RDONLY)) + mnt_flags |= MNT_SB_WRITABLE; newmnt->mnt_flags = mnt_flags; if ((err = graft_tree(newmnt, nd))) goto unlock; @@ -1408,6 +1467,8 @@ long do_mount(char *dev_name, char *dir_ ((char *)data_page)[PAGE_SIZE - 1] = 0; /* Separate the per-mountpoint flags */ + if (flags & MS_RDONLY) + mnt_flags |= MNT_READONLY; if (flags & MS_NOSUID) mnt_flags |= MNT_NOSUID; if (flags & MS_NODEV) diff -puN fs/super.c~C-add-vfsmount-writer_count fs/super.c --- lxc/fs/super.c~C-add-vfsmount-writer_count 2006-08-01 16:35:18.000000000 -0700 +++ lxc-dave/fs/super.c 2006-08-01 16:35:19.000000000 -0700 @@ -93,6 +93,8 @@ static struct super_block *alloc_super(s s->s_qcop = sb_quotactl_ops; s->s_op = &default_op; s->s_time_gran = 1000000000; + atomic_set(&s->s_mnt_writers, 0); + spin_lock_init(&s->s_mnt_writers_lock); } out: return s; @@ -527,6 +529,53 @@ static void mark_files_ro(struct super_b file_list_unlock(); } +static void __sb_mounts_mod_flag(struct super_block *sb, int set, int flag) +{ + struct list_head *p; + + spin_lock(&vfsmount_lock); + list_for_each(p, &sb->s_vfsmounts) { + struct vfsmount *mnt = + list_entry(p, struct vfsmount, mnt_sb_list); + if (set) + mnt->mnt_flags |= flag; + else + mnt->mnt_flags &= ~flag; + } + spin_unlock(&vfsmount_lock); +} + +static void sb_mounts_set_flag(struct super_block *sb, int flag) +{ + __sb_mounts_mod_flag(sb, 1, flag); +} +static void sb_mounts_clear_flag(struct super_block *sb, int flag) +{ + __sb_mounts_mod_flag(sb, 0, flag); +} + +static int sb_remount_ro(struct super_block *sb) +{ + return fs_may_remount_ro(sb); + spin_lock(&sb->s_mnt_writers_lock); + if (atomic_read(&sb->s_mnt_writers) > 0) { + spin_unlock(&sb->s_mnt_writers_lock); + return -EBUSY; + } + + sb_mounts_clear_flag(sb, MNT_SB_WRITABLE); + spin_unlock(&sb->s_mnt_writers_lock); + + return 0; +} + +static void sb_remount_rw(struct super_block *sb) +{ + spin_lock(&sb->s_mnt_writers_lock); + sb_mounts_set_flag(sb, MNT_SB_WRITABLE); + spin_unlock(&sb->s_mnt_writers_lock); +} + /** * do_remount_sb - asks filesystem to change mount options. * @sb: superblock in question @@ -538,7 +587,8 @@ static void mark_files_ro(struct super_b */ int do_remount_sb(struct super_block *sb, int flags, void *data, int force) { - int retval; + int retval = 0; + int sb_started_ro = (sb->s_flags & MS_RDONLY); if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev)) return -EACCES; @@ -549,13 +599,14 @@ int do_remount_sb(struct super_block *sb /* If we are remounting RDONLY and current sb is read/write, make sure there are no rw files opened */ - if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) { + if ((flags & MS_RDONLY) && !sb_started_ro) { if (force) mark_files_ro(sb); - else if (!fs_may_remount_ro(sb)) - return -EBUSY; + else + retval = sb_remount_ro(sb); + if (retval) + return retval; } - if (sb->s_op->remount_fs) { lock_super(sb); retval = sb->s_op->remount_fs(sb, &flags, data); @@ -563,6 +614,9 @@ int do_remount_sb(struct super_block *sb if (retval) return retval; } + if (!(flags & MS_RDONLY) && sb_started_ro) + sb_remount_rw(sb); + sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK); return 0; } @@ -849,6 +903,8 @@ vfs_kern_mount(struct file_system_type * mnt->mnt_mountpoint = mnt->mnt_root; mnt->mnt_parent = mnt; + if (!(mnt->mnt_sb->s_flags & MS_RDONLY)) + mnt->mnt_flags |= MNT_SB_WRITABLE; up_write(&mnt->mnt_sb->s_umount); free_secdata(secdata); return mnt; diff -puN include/linux/fs.h~C-add-vfsmount-writer_count include/linux/fs.h --- lxc/include/linux/fs.h~C-add-vfsmount-writer_count 2006-08-01 16:35:18.000000000 -0700 +++ lxc-dave/include/linux/fs.h 2006-08-01 16:35:19.000000000 -0700 @@ -963,6 +963,8 @@ struct super_block { struct list_head s_io; /* parked for writeback */ struct hlist_head s_anon; /* anonymous dentries for (nfs) exporting */ struct list_head s_vfsmounts; + atomic_t s_mnt_writers; /* vfsmounts with active writers */ + spinlock_t s_mnt_writers_lock; /* taken when mounts change rw state */ struct list_head s_files; struct block_device *s_bdev; diff -puN include/linux/mount.h~C-add-vfsmount-writer_count include/linux/mount.h --- lxc/include/linux/mount.h~C-add-vfsmount-writer_count 2006-08-01 16:35:18.000000000 -0700 +++ lxc-dave/include/linux/mount.h 2006-08-01 16:35:19.000000000 -0700 @@ -27,6 +27,8 @@ struct namespace; #define MNT_NOEXEC 0x04 #define MNT_NOATIME 0x08 #define MNT_NODIRATIME 0x10 +#define MNT_READONLY 0x20 /* does the user want this to be r/o? */ +#define MNT_SB_WRITABLE 0x40 /* does the SB currently allow writes? */ #define MNT_SHRINKABLE 0x100 @@ -44,6 +46,7 @@ struct vfsmount { struct list_head mnt_mounts; /* list of children, anchored here */ struct list_head mnt_child; /* and going through their mnt_child */ atomic_t mnt_count; + atomic_t mnt_writers; int mnt_flags; int mnt_expiry_mark; /* true if marked for expiry */ char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */ @@ -64,6 +67,21 @@ static inline struct vfsmount *mntget(st return mnt; } +static inline int __mnt_is_readonly(struct vfsmount *mnt) +{ + return (mnt->mnt_flags & MNT_READONLY) || + !(mnt->mnt_flags & MNT_SB_WRITABLE); +} + +static inline void __mnt_unmake_readonly(struct vfsmount *mnt) +{ + WARN_ON(!__mnt_is_readonly(mnt)); + mnt->mnt_flags &= ~MNT_READONLY; +} + +extern int mnt_make_readonly(struct vfsmount *mnt); +extern int mnt_want_write(struct vfsmount *mnt); +extern void mnt_drop_write(struct vfsmount *mnt); extern void mntput_no_expire(struct vfsmount *mnt); extern void mnt_pin(struct vfsmount *mnt); extern void mnt_unpin(struct vfsmount *mnt); _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/