diff --git a/src/core/posix_io.c b/src/core/posix_io.c
new file mode 100644
index 00000000..2974a4c8
--- /dev/null
+++ b/src/core/posix_io.c
@@ -0,0 +1,332 @@
+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <gpxe/list.h>
+#include <gpxe/xfer.h>
+#include <gpxe/open.h>
+#include <gpxe/process.h>
+#include <gpxe/posix_io.h>
+
+/** @file
+ *
+ * POSIX-like I/O
+ *
+ * These functions provide traditional blocking I/O semantics.  They
+ * are designed to be used by the PXE TFTP API.  Because they block,
+ * they may not be used by most other portions of the gPXE codebase.
+ */
+
+/** An open file */
+struct posix_file {
+	/** Reference count for this object */
+	struct refcnt refcnt;
+	/** List of open files */
+	struct list_head list;
+	/** File descriptor */
+	int fd;
+	/** Overall status
+	 *
+	 * Set to -EINPROGRESS while data transfer is in progress.
+	 */
+	int rc;
+	/** Data transfer interface */
+	struct xfer_interface xfer;
+	/** Current seek position */
+	size_t pos;
+	/** File size */
+	size_t filesize;
+	/** Received data queue */
+	struct list_head data;
+};
+
+/** List of open files */
+static LIST_HEAD ( posix_files );
+
+/** Minimum file descriptor that will ever be allocated */
+#define POSIX_FD_MIN ( 1 )
+
+/** Maximum file descriptor that will ever be allocated */
+#define POSIX_FD_MAX ( 255 )
+
+/**
+ * Free open file
+ *
+ * @v refcnt		Reference counter
+ */
+static void posix_file_free ( struct refcnt *refcnt ) {
+	struct posix_file *file =
+		container_of ( refcnt, struct posix_file, refcnt );
+	struct io_buffer *iobuf;
+
+	list_for_each_entry ( iobuf, &file->data, list ) {
+		free_iob ( iobuf );
+	}
+	free ( file );
+}
+
+/**
+ * Terminate file data transfer
+ *
+ * @v file		POSIX file
+ * @v rc		Reason for termination
+ */
+static void posix_file_finished ( struct posix_file *file, int rc ) {
+	xfer_nullify ( &file->xfer );
+	xfer_close ( &file->xfer, rc );
+	file->rc = rc;
+}
+
+/**
+ * Handle close() event
+ *
+ * @v xfer		POSIX file data transfer interface
+ * @v rc		Reason for close
+ */
+static void posix_file_xfer_close ( struct xfer_interface *xfer, int rc ) {
+	struct posix_file *file =
+		container_of ( xfer, struct posix_file, xfer );
+
+	posix_file_finished ( file, rc );
+}
+
+/**
+ * Handle seek() event
+ *
+ * @v xfer		POSIX file data transfer interface
+ * @v pos		New position
+ * @ret rc		Return status code
+ */
+static int posix_file_xfer_seek ( struct xfer_interface *xfer, off_t offset,
+				  int whence ) {
+	struct posix_file *file =
+		container_of ( xfer, struct posix_file, xfer );
+
+	switch ( whence ) {
+	case SEEK_SET:
+		file->pos = offset;
+		break;
+	case SEEK_CUR:
+		file->pos += offset;
+		break;
+	}
+
+	if ( file->filesize < file->pos )
+		file->filesize = file->pos;
+
+	return 0;
+}
+
+/**
+ * Handle deliver_iob() event
+ *
+ * @v xfer		POSIX file data transfer interface
+ * @v iobuf		I/O buffer
+ * @ret rc		Return status code
+ */
+static int posix_file_xfer_deliver_iob ( struct xfer_interface *xfer,
+					 struct io_buffer *iobuf ) {
+	struct posix_file *file =
+		container_of ( xfer, struct posix_file, xfer );
+
+	list_add_tail ( &iobuf->list, &file->data );
+	return 0;
+}
+
+/** POSIX file data transfer interface operations */
+static struct xfer_interface_operations posix_file_xfer_operations = {
+	.close		= posix_file_xfer_close,
+	.vredirect	= xfer_vopen,
+	.request	= ignore_xfer_request,
+	.seek		= posix_file_xfer_seek,
+	.alloc_iob	= default_xfer_alloc_iob,
+	.deliver_iob	= posix_file_xfer_deliver_iob,
+	.deliver_raw	= xfer_deliver_as_iob,
+};
+
+/**
+ * Identify file by file descriptor
+ *
+ * @v fd		File descriptor
+ * @ret file		Corresponding file, or NULL
+ */
+static struct posix_file * posix_fd_to_file ( int fd ) {
+	struct posix_file *file;
+
+	list_for_each_entry ( file, &posix_files, list ) {
+		if ( file->fd == fd )
+			return file;
+	}
+	return NULL;
+}
+
+/**
+ * Find an available file descriptor
+ *
+ * @ret fd		File descriptor, or negative error number
+ */
+static int posix_find_free_fd ( void ) {
+	int fd;
+
+	for ( fd = POSIX_FD_MIN ; fd <= POSIX_FD_MAX ; fd++ ) {
+		if ( ! posix_fd_to_file ( fd ) )
+			return fd;
+	}
+	return -ENFILE;
+}
+
+/**
+ * Open file
+ *
+ * @v uri_string	URI string
+ * @ret fd		File descriptor, or negative error number
+ */
+int open ( const char *uri_string ) {
+	struct posix_file *file;
+	int fd;
+	int rc;
+
+	/* Find a free file descriptor to use */
+	fd = posix_find_free_fd();
+	if ( fd < 0 )
+		return fd;
+
+	/* Allocate and initialise structure */
+	file = malloc ( sizeof ( *file ) );
+	if ( ! file )
+		return -ENOMEM;
+	memset ( file, 0, sizeof ( *file ) );
+	file->refcnt.free = posix_file_free;
+	file->fd = fd;
+	file->rc = -EINPROGRESS;
+	xfer_init ( &file->xfer, &posix_file_xfer_operations,
+		    &file->refcnt );
+	INIT_LIST_HEAD ( &file->data );
+
+	/* Open URI on data transfer interface */
+	if ( ( rc = xfer_open_uri ( &file->xfer, uri_string ) ) != 0 )
+		goto err;
+
+	/* Wait for open to succeed or fail */
+	while ( list_empty ( &file->data ) ) {
+		step();
+		if ( file->rc != -EINPROGRESS ) {
+			rc = file->rc;
+			goto err;
+		}
+	}
+
+	/* Add to list of open files.  List takes reference ownership. */
+	list_add ( &file->list, &posix_files );
+	return fd;
+
+ err:
+	posix_file_finished ( file, rc );
+	ref_put ( &file->refcnt );
+	return rc;
+}
+
+/**
+ * Read data from file
+ *
+ * @v buffer		Data buffer
+ * @v offset		Starting offset within data buffer
+ * @v len		Maximum length to read
+ * @ret len		Actual length read, or negative error number
+ */
+ssize_t read_user ( int fd, userptr_t buffer, off_t offset, size_t max_len ) {
+	struct posix_file *file;
+	struct io_buffer *iobuf;
+	size_t frag_len;
+	ssize_t len = 0;
+
+	/* Identify file */
+	file = posix_fd_to_file ( fd );
+	if ( ! file )
+		return -EBADF;
+
+	while ( 1 ) {
+		/* Try to fetch more data if none available */
+		if ( list_empty ( &file->data ) )
+			step();
+		/* Dequeue at most one received I/O buffer into user buffer */
+		list_for_each_entry ( iobuf, &file->data, list ) {
+			frag_len = iob_len ( iobuf );
+			if ( frag_len > max_len )
+				frag_len = max_len;
+			copy_to_user ( buffer, offset, iobuf->data,
+				       frag_len );
+			iob_pull ( iobuf, frag_len );
+			if ( ! iob_len ( iobuf ) )
+				free_iob ( iobuf );
+			file->pos += frag_len;
+			len += frag_len;
+			offset += frag_len;
+			max_len -= frag_len;
+			break;
+		}
+		/* If buffer is full, return */
+		if ( ! max_len )
+			return len;
+		/* If file has completed, return */
+		if ( file->rc != -EINPROGRESS )
+			return ( file->rc ? file->rc : len );
+	}
+}
+
+/**
+ * Determine file size
+ *
+ * @v fd		File descriptor
+ * @ret size		File size, or negative error number
+ */
+ssize_t fsize ( int fd ) {
+	struct posix_file *file;
+
+	/* Identify file */
+	file = posix_fd_to_file ( fd );
+	if ( ! file )
+		return -EBADF;
+
+	return file->filesize;
+}
+
+/**
+ * Close file
+ *
+ * @v fd		File descriptor
+ * @ret rc		Return status code
+ */
+int close ( int fd ) {
+	struct posix_file *file;
+
+	/* Identify file */
+	file = posix_fd_to_file ( fd );
+	if ( ! file )
+		return -EBADF;
+
+	/* Terminate data transfer */
+	posix_file_finished ( file, 0 );
+
+	/* Remove from list of open files and drop reference */
+	list_del ( &file->list );
+	ref_put ( &file->refcnt );
+	return 0;
+}
diff --git a/src/include/gpxe/posix_io.h b/src/include/gpxe/posix_io.h
new file mode 100644
index 00000000..a5cf0c75
--- /dev/null
+++ b/src/include/gpxe/posix_io.h
@@ -0,0 +1,31 @@
+#ifndef _GPXE_POSIX_IO_H
+#define _GPXE_POSIX_IO_H
+
+/** @file
+ *
+ * POSIX-like I/O
+ *
+ */
+
+#include <stdint.h>
+#include <gpxe/uaccess.h>
+
+extern int open ( const char *uri_string );
+extern ssize_t read_user ( int fd, userptr_t buffer,
+			   off_t offset, size_t len );
+extern ssize_t fsize ( int fd );
+extern int close ( int fd );
+
+/**
+ * Read data from file
+ *
+ * @v fd		File descriptor
+ * @v buf		Data buffer
+ * @v len		Maximum length to read
+ * @ret len		Actual length read, or negative error number
+ */
+static inline ssize_t read ( int fd, void *buf, size_t len ) {
+	return read_user ( fd, virt_to_user ( buf ), 0, len );
+}
+
+#endif /* _GPXE_POSIX_IO_H */