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, 2 insertions, 10 deletions

diff --git a/fs/coda/file.c b/fs/coda/file.c
index 466303db2df6..6a347fbc998a 100644
--- a/fs/coda/file.c
+++ b/fs/coda/file.c
@@ -201,8 +201,7 @@ int coda_release(struct inode *coda_inode, struct file *coda_file)
 int coda_fsync(struct file *coda_file, struct dentry *coda_dentry, int datasync)
 {
         struct file *host_file;
-        struct dentry *host_dentry;
-        struct inode *host_inode, *coda_inode = coda_dentry->d_inode;
+        struct inode *coda_inode = coda_dentry->d_inode;
         struct coda_file_info *cfi;
         int err = 0;
 
@@ -214,14 +213,7 @@ int coda_fsync(struct file *coda_file, struct dentry *coda_dentry, int datasync)
         BUG_ON(!cfi || cfi->cfi_magic != CODA_MAGIC);
         host_file = cfi->cfi_container;
 
-        if (host_file->f_op && host_file->f_op->fsync) {
-                host_dentry = host_file->f_path.dentry;
-                host_inode = host_dentry->d_inode;
-                mutex_lock(&host_inode->i_mutex);
-                err = host_file->f_op->fsync(host_file, host_dentry, datasync);
-                mutex_unlock(&host_inode->i_mutex);
-        }
-
+        err = vfs_fsync(host_file, host_file->f_path.dentry, datasync);
         if ( !err && !datasync ) {
                 lock_kernel();
                 err = venus_fsync(coda_inode->i_sb, coda_i2f(coda_inode));