Re: nfs3 dentry encoding

[Olaf Kirch <okir@suse.de>]

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On Thu, May 27, 2004 at 09:09:49PM +1000, Neil Brown wrote:
> Hmmm, just as well someone is watching over me!  Thanks.

I'm currently looking into a failure with a Solaris 9 running connectathon
against a 2.6 Linux server. It fails in a test case doing a readdirplus
of a large directory, because it scribbles the offset value into
random memory locations (usually at page offset 0)

See the attached patch, which I also posted in a follow-up to
your message to to linux-kernel.

The first hunk is rather cosmetic; rq_res is cleared by a memset
so there's not need to zero the offset pointer(s) here. In fact
we don't initialize them in readdirplus anyway.

Olaf
-- 
Olaf Kirch     |  The Hardware Gods hate me.
okir@suse.de   |
---------------+ 

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Index: linux-2.6.5/fs/nfsd/nfs3proc.c
===================================================================
--- linux-2.6.5.orig/fs/nfsd/nfs3proc.c	2004-05-27 12:22:43.000000000 +0200
+++ linux-2.6.5/fs/nfsd/nfs3proc.c	2004-05-27 12:34:40.000000000 +0200
@@ -437,7 +437,6 @@
 	resp->buflen = count;
 	resp->common.err = nfs_ok;
 	resp->buffer = argp->buffer;
-	resp->offset = NULL;
 	resp->rqstp = rqstp;
 	nfserr = nfsd_readdir(rqstp, &resp->fh, (loff_t*) &argp->cookie, 
 					&resp->common, nfs3svc_encode_entry);
Index: linux-2.6.5/fs/nfsd/nfs3xdr.c
===================================================================
--- linux-2.6.5.orig/fs/nfsd/nfs3xdr.c	2004-05-27 12:22:43.000000000 +0200
+++ linux-2.6.5/fs/nfsd/nfs3xdr.c	2004-05-27 12:39:09.000000000 +0200
@@ -887,8 +887,18 @@
 	int		elen;		/* estimated entry length in words */
 	int		num_entry_words = 0;	/* actual number of words */
 
-	if (cd->offset)
-		xdr_encode_hyper(cd->offset, (u64) offset);
+	if (cd->offset) {
+		u64 offset64 = offset;
+
+		if (unlikely(cd->offset1)) {
+			/* we ended up with offset on a page boundary */
+			*cd->offset = htonl(offset64 >> 32);
+			*cd->offset1 = htonl(offset64 & 0xffffffff);
+			cd->offset1 = NULL;
+		} else {
+			xdr_encode_hyper(cd->offset, (u64) offset);
+		}
+	}
 
 	/*
 	dprintk("encode_entry(%.*s @%ld%s)\n",
@@ -969,17 +979,32 @@
 			/* update offset */
 			cd->offset = cd->buffer + (cd->offset - tmp);
 		} else {
+			unsigned int offset_r = (cd->offset - tmp) << 2;
+
+			/* update pointer to offset location.
+			 * This is a 64bit quantity, so we need to
+			 * deal with 3 cases:
+			 *  -	entirely in first page
+			 *  -	entirely in second page
+			 *  -	4 bytes in each page
+			 */
+			if (offset_r + 8 <= len1) {
+				cd->offset = p + (cd->offset - tmp);
+			} else if (offset_r >= len1) {
+				cd->offset -= len1 >> 2;
+			} else {
+				/* sitting on the fence */
+				BUG_ON(offset_r != len1 - 4);
+				cd->offset = p + (cd->offset - tmp);
+				cd->offset1 = tmp;
+			}
+
 			len2 = (num_entry_words << 2) - len1;
 
 			/* move from temp page to current and next pages */
 			memmove(p, tmp, len1);
 			memmove(tmp, (caddr_t)tmp+len1, len2);
 
-			/* update offset */
-			if (((cd->offset - tmp) << 2) <= len1)
-				cd->offset = p + (cd->offset - tmp);
-			else
-				cd->offset -= len1 >> 2;
 			p = tmp + (len2 >> 2);
 		}
 	}
Index: linux-2.6.5/include/linux/nfsd/xdr3.h
===================================================================
--- linux-2.6.5.orig/include/linux/nfsd/xdr3.h	2004-05-27 12:22:43.000000000 +0200
+++ linux-2.6.5/include/linux/nfsd/xdr3.h	2004-05-27 12:28:20.000000000 +0200
@@ -183,6 +183,7 @@
 	u32 *			buffer;
 	int			buflen;
 	u32 *			offset;
+	u32 *			offset1;
 	struct svc_rqst *	rqstp;
 
 };