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Message-ID: <Pine.LNX.4.44L0.0812221102190.18968-100000@netrider.rowland.org>
Date: Mon, 22 Dec 2008 11:07:26 -0500 (EST)
From: Alan Stern <stern@...land.harvard.edu>
To: Christoph Hellwig <hch@....de>
cc: Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH, RFC] add a vfs_fsync helper
On Mon, 22 Dec 2008, Christoph Hellwig wrote:
> 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.
> Index: xfs/fs/sync.c
> ===================================================================
> --- xfs.orig/fs/sync.c 2008-12-19 15:02:53.942907780 +0100
> +++ xfs/fs/sync.c 2008-12-21 12:22:17.180896085 +0100
> @@ -75,14 +75,39 @@
> return ret;
> }
>
> -long do_fsync(struct file *file, int datasync)
> +/**
> + * vfs_fsync - perform a fsync or fdatasync on a file
> + * @file: file to sync
> + * @dentry: dentry of @file
> + * @data: only perform a fdatasync operation
> + *
> + * Write back data and metadata for @file to disk. If @datasync is
> + * set only metadata needed to access modified file data is written.
> + *
> + * In case this function is called from nfsd @file may be %NULL and
> + * only @dentry is set. This can only happen when the filesystem
> + * implements the export_operations API.
> + */
> +int vfs_fsync(struct file *file, struct dentry *dentry, int datasync)
> {
> - int ret;
> - int err;
> - struct address_space *mapping = file->f_mapping;
> + struct file_operations *fop;
> + struct address_space *mapping;
> + int err, ret;
> +
> + /*
> + * Get mapping and operations from the file in case we have
> + * as file, or get the default values for them in case we
> + * don't have a struct file available. Damn nfsd..
> + */
> + if (file) {
> + mapping = file->f_mapping;
> + fop = file->f_op;
> + } else {
> + mapping = dentry->d_inode->i_mapping;
> + fop = dentry->d_inode->i_fop;
> + }
>
> - if (!file->f_op || !file->f_op->fsync) {
> - /* Why? We can still call filemap_fdatawrite */
> + if (!fop || !fop->fsync) {
> ret = -EINVAL;
> goto out;
> }
> @@ -94,7 +119,7 @@
> * livelocks in fsync_buffers_list().
> */
> mutex_lock(&mapping->host->i_mutex);
> - err = file->f_op->fsync(file, file->f_path.dentry, datasync);
> + err = fop->fsync(file, dentry, datasync);
> if (!ret)
> ret = err;
> mutex_unlock(&mapping->host->i_mutex);
> @@ -105,14 +130,14 @@
> return ret;
> }
>
> -static long __do_fsync(unsigned int fd, int datasync)
> +static int do_fsync(unsigned int fd, int datasync)
> {
> struct file *file;
> int ret = -EBADF;
>
> file = fget(fd);
> if (file) {
> - ret = do_fsync(file, datasync);
> + ret = vfs_fsync(file, file->f_path.dentry, datasync);
> fput(file);
> }
> return ret;
> @@ -120,12 +145,12 @@
>
> asmlinkage long sys_fsync(unsigned int fd)
> {
> - return __do_fsync(fd, 0);
> + return do_fsync(fd, 0);
> }
>
> asmlinkage long sys_fdatasync(unsigned int fd)
> {
> - return __do_fsync(fd, 1);
> + return do_fsync(fd, 1);
> }
>
> /*
> Index: xfs/drivers/usb/gadget/file_storage.c
> ===================================================================
> --- xfs.orig/drivers/usb/gadget/file_storage.c 2008-12-21 12:26:53.254894542 +0100
> +++ xfs/drivers/usb/gadget/file_storage.c 2008-12-21 12:28:08.914896191 +0100
> @@ -1863,26 +1863,10 @@
> static int fsync_sub(struct lun *curlun)
> {
> struct file *filp = curlun->filp;
> - struct inode *inode;
> - int rc, err;
>
> if (curlun->ro || !filp)
> return 0;
> - if (!filp->f_op->fsync)
> - return -EINVAL;
> -
> - inode = filp->f_path.dentry->d_inode;
> - mutex_lock(&inode->i_mutex);
> - rc = filemap_fdatawrite(inode->i_mapping);
> - err = filp->f_op->fsync(filp, filp->f_path.dentry, 1);
> - if (!rc)
> - rc = err;
> - err = filemap_fdatawait(inode->i_mapping);
> - if (!rc)
> - rc = err;
> - mutex_unlock(&inode->i_mutex);
> - VLDBG(curlun, "fdatasync -> %d\n", rc);
> - return rc;
> + return vfs_fsync(filp, filp->f_path.dentry->d_inode, 1);
> }
This won't work unless vfs_fsync() is EXPORTed.
Alan Stern
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