NFS mountned directory and apache2 (2.5.47)

It does not change anything on the brokeness of apache2 (or maybe glibc). It must be able to revert to read/write loop if sendfile fails with EINVAL. There is no guarantee that existing sendfile() API means that you can use it with all filesystems.
Best regards,
Petr Vandrovec [email protected]

> It does not change anything on the brokeness of apache2 (or > maybe glibc). It must be able to revert to read/write loop if > sendfile fails with EINVAL. There is no guarantee that existing > sendfile() API means that you can use it with all filesystems.

I disagree. Sendfile can *always* be emulated using the standard file 'read' method.

For most filesystems, that means just reading directly from the page cache, and that is precisely what generic_file_sendfile() does. IIRC, the sendfile() inode op was added so that those few filesystems which don't support direct reading of the page cache could roll their own.

Cheers,
Trond

Linus removed that in early 2.5 because it led to kmap() deadlocks. sendfile can fail with EINVAL and userspace must not rely on it working on any object.

> Linus removed that in early 2.5 because it led to kmap() > deadlocks. sendfile can fail with EINVAL and userspace must > not rely on it working on any object.

Fair enough. The kernel may not be the appropriate place for providing such an emulation, but there's no reason why glibc shouldn't be able to do so for the case where sendfile returns EINVAL.

However none of this changes the matter of the NFS client. The latter *does* support a pagecache, and so the one-line patch is appropriate.

Cheers,
Trond

*nod*

just a little bit more then one line :) nfs needs to do the same revalidation as in nfs_file_read and then call generic_file_sendfile.

> just a little bit more then one line :) nfs needs to do the > same revalidation as in nfs_file_read and then call > generic_file_sendfile.

Duh, I must have eaten a bad mushroom at dinner. Thanks for staying awake...

The correct patch is of course as appended.

Cheers,
Trond

@@ -35,6 +35,7 @@
 #define NFSDBG_FACILITY		NFSDBG_FILE
 
 static int  nfs_file_mmap(struct file *, struct vm_area_struct *);
+static ssize_t nfs_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void *);
 static ssize_t nfs_file_read(struct kiocb *, char *, size_t, loff_t);
 static ssize_t nfs_file_write(struct kiocb *, const char *, size_t, loff_t);
 static int  nfs_file_flush(struct file *);

@@ -52,6 +53,7 @@
 	.release	= nfs_release,
 	.fsync		= nfs_fsync,
 	.lock		= nfs_lock,
+	.sendfile	= nfs_file_sendfile,
 };
 
 struct inode_operations nfs_file_inode_operations = {

@@ -102,6 +104,24 @@
 	return result;
 }
 
+static ssize_t
+nfs_file_sendfile(struct file *filp, loff_t *ppos, size_t count,
+		read_actor_t actor, void *target)
+{
+	struct dentry *dentry = filp->f_dentry;
+	struct inode *inode = dentry->d_inode;
+	ssize_t res;
+
+	dfprintk(VFS, "nfs: sendfile(%s/%s, %lu@%Lu)\n",
+		dentry->d_parent->d_name.name, dentry->d_name.name,
+		(unsigned long) count, (unsigned long long) *ppos);
+
+	res = nfs_revalidate_inode(NFS_SERVER(inode), inode);
+	if (!res)
+		res = generic_file_sendfile(filp, ppos, count, actor, target);
+	return res;
+}
+
 static int
 nfs_file_mmap(struct file * file, struct vm_area_struct * vma)
 {

In article <[email protected]>,

Now that I think we've fixed the deadlocks a different way, we _might_ be able to re-introduce a more generic sendfile().

We should also change the name of the dang thing at least internally, since it has very little to do with sending a file any more. And furthermore we should probably introduce an internal file operation that is the reverse of our misnamed "sendfile", ie a "receive actor" (we already have the notion of actors, but we don't use them for receiving directly into a "struct file *").

Then we could actually do a real "copyfile()", by just matching up the source file "sendfile()" function with the destination file "receive actor" function and letting it rip. That should allow true "move the page cache page from one file to another" copies of files, for example.

Linus