[PATCH v3 06/11] Add helpers to read/write to a file through the chrooted thread

[Trond Myklebust <trondmy@gmail.com>]

Add helper functions to do synchronous I/O to a nfsd filesystem pseudofile
from inside the chrooted environment. This ensures that calls to kern_path()
in knfsd resolves to paths that are relative to the nfsd root directory.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 support/include/nfsd_path.h |  3 ++
 support/misc/nfsd_path.c    | 84 +++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/support/include/nfsd_path.h b/support/include/nfsd_path.h
index db9b41a179ad..f4a7f0a4337f 100644
--- a/support/include/nfsd_path.h
+++ b/support/include/nfsd_path.h
@@ -13,4 +13,7 @@ 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);
 
+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);
+
 #endif
diff --git a/support/misc/nfsd_path.c b/support/misc/nfsd_path.c
index fe2c011b1521..55bca9bdf4bd 100644
--- a/support/misc/nfsd_path.c
+++ b/support/misc/nfsd_path.c
@@ -166,3 +166,87 @@ nfsd_path_lstat(const char *pathname, struct stat *statbuf)
 		return xlstat(pathname, statbuf);
 	return nfsd_run_stat(nfsd_wq, nfsd_lstatfunc, pathname, statbuf);
 }
+
+struct nfsd_read_data {
+	int fd;
+	char *buf;
+	size_t len;
+	ssize_t ret;
+	int err;
+};
+
+static void
+nfsd_readfunc(void *data)
+{
+	struct nfsd_read_data *d = data;
+
+	d->ret = read(d->fd, d->buf, d->len);
+	if (d->ret < 0)
+		d->err = errno;
+}
+
+static ssize_t
+nfsd_run_read(struct xthread_workqueue *wq, int fd, char *buf, size_t len)
+{
+	struct nfsd_read_data data = {
+		fd,
+		buf,
+		len,
+		0,
+		0
+	};
+	xthread_work_run_sync(wq, nfsd_readfunc, &data);
+	if (data.ret < 0)
+		errno = data.err;
+	return data.ret;
+}
+
+ssize_t
+nfsd_path_read(int fd, char *buf, size_t len)
+{
+	if (!nfsd_wq)
+		return read(fd, buf, len);
+	return nfsd_run_read(nfsd_wq, fd, buf, len);
+}
+
+struct nfsd_write_data {
+	int fd;
+	const char *buf;
+	size_t len;
+	ssize_t ret;
+	int err;
+};
+
+static void
+nfsd_writefunc(void *data)
+{
+	struct nfsd_write_data *d = data;
+
+	d->ret = write(d->fd, d->buf, d->len);
+	if (d->ret < 0)
+		d->err = errno;
+}
+
+static ssize_t
+nfsd_run_write(struct xthread_workqueue *wq, int fd, const char *buf, size_t len)
+{
+	struct nfsd_write_data data = {
+		fd,
+		buf,
+		len,
+		0,
+		0
+	};
+	xthread_work_run_sync(wq, nfsd_writefunc, &data);
+	if (data.ret < 0)
+		errno = data.err;
+	return data.ret;
+}
+
+ssize_t
+nfsd_path_write(int fd, const char *buf, size_t len)
+{
+	if (!nfsd_wq)
+		return write(fd, buf, len);
+	return nfsd_run_write(nfsd_wq, fd, buf, len);
+}
-- 
2.21.0