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: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 4 insertions, 0 deletions

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 8d1c2d1a159b..9eb8086ea841 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -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);
 }
 
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index a6faee562b31..0d20fd161225 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -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;