[PATCH v3 10/11] Add a helper for resolving symlinked nfsd paths via realpath()

[Trond Myklebust <trondmy@gmail.com>]

Add a helper to resolve symlinked nfsd paths when the user has set the
"[exports] rootdir" nfs.conf option.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 support/include/nfsd_path.h |  2 ++
 support/misc/nfsd_path.c    | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/support/include/nfsd_path.h b/support/include/nfsd_path.h
index f4a7f0a4337f..ca2570a92e68 100644
--- a/support/include/nfsd_path.h
+++ b/support/include/nfsd_path.h
@@ -13,6 +13,8 @@ char *		nfsd_path_prepend_dir(const char *dir, const char *pathname);
 int 		nfsd_path_stat(const char *pathname, struct stat *statbuf);
 int 		nfsd_path_lstat(const char *pathname, struct stat *statbuf);
 
+char *		nfsd_realpath(const char *path, char *resolved_path);
+
 ssize_t		nfsd_path_read(int fd, char *buf, size_t len);
 ssize_t		nfsd_path_write(int fd, const char *buf, size_t len);
 
diff --git a/support/misc/nfsd_path.c b/support/misc/nfsd_path.c
index 8ddafd65ab76..2f41a793c534 100644
--- a/support/misc/nfsd_path.c
+++ b/support/misc/nfsd_path.c
@@ -1,6 +1,7 @@
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <stdlib.h>
 #include <unistd.h>
 
 #include "config.h"
@@ -169,6 +170,40 @@ nfsd_path_lstat(const char *pathname, struct stat *statbuf)
 	return nfsd_run_stat(nfsd_wq, nfsd_lstatfunc, pathname, statbuf);
 }
 
+struct nfsd_realpath_data {
+	const char *pathname;
+	char *resolved;
+	int err;
+};
+
+static void
+nfsd_realpathfunc(void *data)
+{
+	struct nfsd_realpath_data *d = data;
+
+	d->resolved = realpath(d->pathname, d->resolved);
+	if (!d->resolved)
+		d->err = errno;
+}
+
+char *
+nfsd_realpath(const char *path, char *resolved_path)
+{
+	struct nfsd_realpath_data data = {
+		path,
+		resolved_path,
+		0
+	};
+
+	if (!nfsd_wq)
+		return realpath(path, resolved_path);
+
+	xthread_work_run_sync(nfsd_wq, nfsd_realpathfunc, &data);
+	if (!data.resolved)
+		errno = data.err;
+	return data.resolved;
+}
+
 struct nfsd_read_data {
 	int fd;
 	char *buf;
-- 
2.21.0