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Commit 11b4d66e authored by Chuck Lever's avatar Chuck Lever Committed by J. Bruce Fields
Browse files

NFSD: Handle full-length symlinks 



I've given up on the idea of zero-copy handling of SYMLINK on the
server side. This is because the Linux VFS symlink API requires the
symlink pathname to be in a NUL-terminated kmalloc'd buffer. The
NUL-termination is going to be problematic (watching out for
landing on a page boundary and dealing with a 4096-byte pathname).

I don't believe that SYMLINK creation is on a performance path or is
requested frequently enough that it will cause noticeable CPU cache
pollution due to data copies.

There will be two places where a transport callout will be necessary
to fill in the rqstp: one will be in the svc_fill_symlink_pathname()
helper that is used by NFSv2 and NFSv3, and the other will be in
nfsd4_decode_create().

Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent 3fd9557a

fs/nfsd/nfs3proc.c

+2 −0
Original line number Diff line number Diff line
@@ -290,6 +290,7 @@ nfsd3_proc_symlink(struct svc_rqst *rqstp) 
		RETURN_STATUS(nfserr_nametoolong);



	argp->tname = svc_fill_symlink_pathname(rqstp, &argp->first,

						page_address(rqstp->rq_arg.pages[0]),

						argp->tlen);

	if (IS_ERR(argp->tname))

		RETURN_STATUS(nfserrno(PTR_ERR(argp->tname)));
@@ -303,6 +304,7 @@ nfsd3_proc_symlink(struct svc_rqst *rqstp) 
	fh_init(&resp->fh, NFS3_FHSIZE);

	nfserr = nfsd_symlink(rqstp, &resp->dirfh, argp->fname, argp->flen,

						   argp->tname, &resp->fh);

	kfree(argp->tname);

	RETURN_STATUS(nfserr);

}

fs/nfsd/nfsproc.c

+2 −0
Original line number Diff line number Diff line
@@ -454,6 +454,7 @@ nfsd_proc_symlink(struct svc_rqst *rqstp) 
		return nfserr_nametoolong;



	argp->tname = svc_fill_symlink_pathname(rqstp, &argp->first,

						page_address(rqstp->rq_arg.pages[0]),

						argp->tlen);

	if (IS_ERR(argp->tname))

		return nfserrno(PTR_ERR(argp->tname));
@@ -466,6 +467,7 @@ nfsd_proc_symlink(struct svc_rqst *rqstp) 
	nfserr = nfsd_symlink(rqstp, &argp->ffh, argp->fname, argp->flen,

						 argp->tname, &newfh);



	kfree(argp->tname);

	fh_put(&argp->ffh);

	fh_put(&newfh);

	return nfserr;

include/linux/sunrpc/svc.h

+2 −1
Original line number Diff line number Diff line
@@ -499,7 +499,8 @@ unsigned int svc_fill_write_vector(struct svc_rqst *rqstp, 
					 struct page **pages,

					 struct kvec *first, size_t total);

char		  *svc_fill_symlink_pathname(struct svc_rqst *rqstp,

					     struct kvec *first, size_t total);

					     struct kvec *first, void *p,

					     size_t total);



#define	RPC_MAX_ADDRBUFLEN	(63U)

net/sunrpc/svc.c

+25 −42
Original line number Diff line number Diff line
@@ -1577,65 +1577,48 @@ EXPORT_SYMBOL_GPL(svc_fill_write_vector); 
 * svc_fill_symlink_pathname - Construct pathname argument for VFS symlink call

 * @rqstp: svc_rqst to operate on

 * @first: buffer containing first section of pathname

 * @p: buffer containing remaining section of pathname

 * @total: total length of the pathname argument

 *

 * Returns pointer to a NUL-terminated string, or an ERR_PTR. The buffer is

 * released automatically when @rqstp is recycled.

 * The VFS symlink API demands a NUL-terminated pathname in mapped memory.

 * Returns pointer to a NUL-terminated string, or an ERR_PTR. Caller must free

 * the returned string.

 */

char *svc_fill_symlink_pathname(struct svc_rqst *rqstp, struct kvec *first,

				size_t total)

				void *p, size_t total)

{

	struct xdr_buf *arg = &rqstp->rq_arg;

	struct page **pages;

	char *result;



	/* VFS API demands a NUL-terminated pathname. This function

	 * uses a page from @rqstp as the pathname buffer, to enable

	 * direct placement. Thus the total buffer size is PAGE_SIZE.

	 * Space in this buffer for NUL-termination requires that we

	 * cap the size of the returned symlink pathname just a

	 * little early.

	 */

	if (total > PAGE_SIZE - 1)

		return ERR_PTR(-ENAMETOOLONG);



	/* Some types of transport can present the pathname entirely

	 * in rq_arg.pages. If not, then copy the pathname into one

	 * page.

	 */

	pages = arg->pages;

	WARN_ON_ONCE(arg->page_base != 0);

	if (first->iov_base == 0) {

		result = page_address(*pages);

		result[total] = '\0';

	} else {

	size_t len, remaining;

		char *dst;

	char *result, *dst;



	result = kmalloc(total + 1, GFP_KERNEL);

	if (!result)

		return ERR_PTR(-ESERVERFAULT);



		result = page_address(*(rqstp->rq_next_page++));

	dst = result;

	remaining = total;



	len = min_t(size_t, total, first->iov_len);

	if (len) {

		memcpy(dst, first->iov_base, len);

		dst += len;

		remaining -= len;

	}



		/* No more than one page left */

	if (remaining) {

		len = min_t(size_t, remaining, PAGE_SIZE);

			memcpy(dst, page_address(*pages), len);

		memcpy(dst, p, len);

		dst += len;

	}



	*dst = '\0';

	}



	/* Sanity check: we don't allow the pathname argument to

	/* Sanity check: Linux doesn't allow the pathname argument to

	 * contain a NUL byte.

	 */

	if (strlen(result) != total)

	if (strlen(result) != total) {

		kfree(result);

		return ERR_PTR(-EINVAL);

	}

	return result;

}

EXPORT_SYMBOL_GPL(svc_fill_symlink_pathname);