add a vfs_fsync helper

Fsync currently has a fdatawrite/fdatawait pair around the method call,
and a mutex_lock/unlock of the inode mutex.  All callers of fsync have
to duplicate this, but we have a few and most of them don't quite get
it right.  This patch adds a new vfs_fsync that takes care of this.
It's a little more complicated as usual as ->fsync might get a NULL file
pointer and just a dentry from nfsd, but otherwise gets afile and we
want to take the mapping and file operations from it when it is there.

Notes on the fsync callers:

 - ecryptfs wasn't calling filemap_fdatawrite / filemap_fdatawait on the
   	lower file
 - coda wasn't calling filemap_fdatawrite / filemap_fdatawait on the host
	file, and returning 0 when ->fsync was missing
 - shm wasn't calling either filemap_fdatawrite / filemap_fdatawait nor
   taking i_mutex.  Now given that shared memory doesn't have disk
   backing not doing anything in fsync seems fine and I left it out of
   the vfs_fsync conversion for now, but in that case we might just
   not pass it through to the lower file at all but just call the no-op
   simple_sync_file directly.

[and now actually export vfs_fsync]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 3 insertions, 32 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 5245a3965004..44aa92aba891 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -744,45 +744,16 @@ nfsd_close(struct file *filp)
         fput(filp);
 }
 
-/*
- * Sync a file
- * As this calls fsync (not fdatasync) there is no need for a write_inode
- * after it.
- */
-static inline int nfsd_dosync(struct file *filp, struct dentry *dp,
-                              const struct file_operations *fop)
-{
-        struct inode *inode = dp->d_inode;
-        int (*fsync) (struct file *, struct dentry *, int);
-        int err;
-
-        err = filemap_fdatawrite(inode->i_mapping);
-        if (err == 0 && fop && (fsync = fop->fsync))
-                err = fsync(filp, dp, 0);
-        if (err == 0)
-                err = filemap_fdatawait(inode->i_mapping);
-
-        return err;
-}
-        
-
 static int
 nfsd_sync(struct file *filp)
 {
-        int err;
-        struct inode *inode = filp->f_path.dentry->d_inode;
-        dprintk("nfsd: sync file %s\n", filp->f_path.dentry->d_name.name);
-        mutex_lock(&inode->i_mutex);
-        err=nfsd_dosync(filp, filp->f_path.dentry, filp->f_op);
-        mutex_unlock(&inode->i_mutex);
-
-        return err;
+        return vfs_fsync(filp, filp->f_path.dentry, 0);
 }
 
 int
-nfsd_sync_dir(struct dentry *dp)
+nfsd_sync_dir(struct dentry *dentry)
 {
-        return nfsd_dosync(NULL, dp, dp->d_inode->i_fop);
+        return vfs_fsync(NULL, dentry, 0);
 }
 
 /*