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: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
fs/nfsd/nfs3proc.c | 2 +
fs/nfsd/nfsproc.c | 2 +
include/linux/sunrpc/svc.h | 3 +-
net/sunrpc/svc.c | 67 ++++++++++++++++----------------------------
4 files changed, 31 insertions(+), 43 deletions(-)
diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 8d1c2d1a..9eb8086 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -290,6 +290,7 @@
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 @@
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);
}
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index a6faee5..0d20fd1 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -454,6 +454,7 @@
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 @@
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;
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 43f88bd..73e130a 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -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)
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 2194ed5..d13e05f 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1577,65 +1577,48 @@ unsigned int svc_fill_write_vector(struct svc_rqst *rqstp, struct page **pages,
* 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);
+ size_t len, remaining;
+ char *result, *dst;
- /* 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;
+ result = kmalloc(total + 1, GFP_KERNEL);
+ if (!result)
+ return ERR_PTR(-ESERVERFAULT);
- result = page_address(*(rqstp->rq_next_page++));
- dst = result;
- remaining = total;
+ dst = result;
+ remaining = total;
- len = min_t(size_t, total, first->iov_len);
+ 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);
- dst += len;
- }
-
- *dst = '\0';
+ if (remaining) {
+ len = min_t(size_t, remaining, PAGE_SIZE);
+ memcpy(dst, p, len);
+ dst += len;
}
- /* Sanity check: we don't allow the pathname argument to
+ *dst = '\0';
+
+ /* 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);
--
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