vfs: add O_NOCMTIME

Add a O_NOCMTIME flag which prevents inode time updates on writes and
can greatly reduce the IO overhead of writes to allocated and
initialized regions of files.

ceph servers can have loads where they perform O_DIRECT overwrites of
allocated file data and then sync to make sure that the O_DIRECT writes
are flushed from write caches.  If the writes dirty the inode with mtime
updates then the syncs also write out the metadata needed to track the
inodes which can add significant iop and latency overhead.

The ceph servers don't use mtime at all.  They're using the local file
system as a backing store and any backups would be driven by their upper
level ceph metadata.

In simple tests a O_DIRECT|O_NOCMTIME overwriting write followed by a
sync went from 2 serial write round trips to 1 in XFS and from 4 serial
IO round trips to 1 in ext4.

file_update_time() is changed to call a file_is_nocmtime() helper which
tests the file flag in addition to testing the inode's S_NOCMTIME flag.
It doesn't check FMODE_NOCMTIME because that's only used by XFS to
trigger private flags which trigger private flags which do other things.

O_NOCMTIME can only be used if the mount has its MNT_NOCMTIME flag set.
This requires priviledged intervention to testify that mtime isn't
critical to, say, backup infrastructure or NFS server consistency
guarantees.

Signed-off-by: Zach Brown <zab@zabbo.net>

diff --git a/fs/fcntl.c b/fs/fcntl.c
index ee85cd4e136abbff33409fb018343028d21578e2..eaa5d1de36d6c1732f9b3c5106eeefc754e300bb 100644 (file)
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -22,12 +22,30 @@
 #include <linux/pid_namespace.h>
 #include <linux/user_namespace.h>
 #include <linux/shmem_fs.h>
+#include <linux/mount.h>
 
 #include <asm/poll.h>
 #include <asm/siginfo.h>
 #include <asm/uaccess.h>
 
-#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME)
+#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME | \
+                   O_NOCMTIME)
+
+/*
+ * O_NOATIME and O_NOCMTIME can only be set by the ownder or superuser.
+ * And O_NOCMTIME requires MNT_NOCMTIME.
+ */
+bool forbid_o_notime(struct inode *inode, struct vfsmount *mnt,
+                    unsigned long flags)
+{
+       if ((flags & (O_NOATIME|O_NOCMTIME)) && !inode_owner_or_capable(inode))
+               return true;
+
+       if ((flags & O_NOCMTIME) && !(mnt->mnt_flags & MNT_NOCMTIME))
+               return true;
+
+       return false;
+}
 
 static int setfl(int fd, struct file * filp, unsigned long arg)
 {
@@ -41,10 +59,8 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
        if (((arg ^ filp->f_flags) & O_APPEND) && IS_APPEND(inode))
                return -EPERM;
 
-       /* O_NOATIME can only be set by the owner or superuser */
-       if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
-               if (!inode_owner_or_capable(inode))
-                       return -EPERM;
+       if (forbid_o_notime(inode, filp->f_path.mnt, arg & ~filp->f_flags))
+               return -EPERM;
 
        /* required for strict SunOS emulation */
        if (O_NONBLOCK != O_NDELAY)
@@ -740,7 +756,7 @@ static int __init fcntl_init(void)
         * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
         * is defined as O_NONBLOCK on some platforms and not on others.
         */
-       BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
+       BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
                O_RDONLY        | O_WRONLY      | O_RDWR        |
                O_CREAT         | O_EXCL        | O_NOCTTY      |
                O_TRUNC         | O_APPEND      | /* O_NONBLOCK | */
@@ -748,7 +764,7 @@ static int __init fcntl_init(void)
                O_DIRECT        | O_LARGEFILE   | O_DIRECTORY   |
                O_NOFOLLOW      | O_NOATIME     | O_CLOEXEC     |
                __FMODE_EXEC    | O_PATH        | __O_TMPFILE   |
-               __FMODE_NONOTIFY
+               __FMODE_NONOTIFY| O_NOCMTIME
                ));
 
        fasync_cache = kmem_cache_create("fasync_cache",

diff --git a/fs/inode.c b/fs/inode.c
index ea37cd17b53f0c98b47e2e626b9ff2a9b6e5699b..b643dd0d42a7a4c14c840a43eeb2346e2bf75f8e 100644 (file)
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1721,7 +1721,7 @@ int file_update_time(struct file *file)
        int ret;
 
        /* First try to exhaust all avenues to not sync */
-       if (IS_NOCMTIME(inode))
+       if (file_is_nocmtime(file))
                return 0;
 
        now = current_fs_time(inode->i_sb);

diff --git a/fs/namei.c b/fs/namei.c
index fe30d3be43a8b381d3b9ac3016b28531996f91b7..8ecebca0c7a22e6cfc26f8a102e1c3bddd849d76 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2617,8 +2617,7 @@ static int may_open(struct path *path, int acc_mode, int flag)
                        return -EPERM;
        }
 
-       /* O_NOATIME can only be set by the owner or superuser */
-       if (flag & O_NOATIME && !inode_owner_or_capable(inode))
+       if (forbid_o_notime(inode, path->mnt, flag))
                return -EPERM;
 
        return 0;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 35ec87e490b1a41ff0bc3ba20b06ac9d958f972a..dd92eeb7e62c3a1ef523b7ce9be6363ad5f3ab8d 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1471,6 +1471,8 @@ static inline void sb_start_intwrite(struct super_block *sb)
 
 
 extern bool inode_owner_or_capable(const struct inode *inode);
+extern bool forbid_o_notime(struct inode *inode, struct vfsmount *mnt,
+                           unsigned long flags);
 
 /*
  * VFS helper functions..
@@ -2950,6 +2952,11 @@ static inline bool is_root_inode(struct inode *inode)
        return inode == inode->i_sb->s_root->d_inode;
 }
 
+static inline bool file_is_nocmtime(struct file *file)
+{
+       return IS_NOCMTIME(file_inode(file)) || (file->f_flags & O_NOCMTIME);
+}
+
 static inline bool dir_emit(struct dir_context *ctx,
                            const char *name, int namelen,
                            u64 ino, unsigned type)

diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index e063effe0cc18f0976f01b49cb56c3aeac47bf69..ed7b2e11404e33bf0a592d6bfb94aedaa52eb4d8 100644 (file)
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -88,6 +88,10 @@
 #define __O_TMPFILE    020000000
 #endif
 
+#ifndef O_NOCMTIME
+#define O_NOCMTIME     040000000
+#endif
+
 /* a horrid kludge trying to make sure that this will fail on old kernels */
 #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
 #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT)