gpxe/src/arch/i386/interface/pxe/pxe_tftp.c

/** @file
 *
 * PXE TFTP API
 *
 */

/*
 * Copyright (C) 2004 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.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <byteswap.h>
#include <gpxe/uaccess.h>
#include <gpxe/in.h>
#include <gpxe/tftp.h>
#include <gpxe/xfer.h>
#include <gpxe/open.h>
#include <gpxe/process.h>
#include <pxe.h>

/** A PXE TFTP connection */
struct pxe_tftp_connection {
	/** Data transfer interface */
	struct xfer_interface xfer;
	/** Data buffer */
	userptr_t buffer;
	/** Size of data buffer */
	size_t size;
	/** Starting offset of data buffer */
	size_t start;
	/** File position */
	size_t offset;
	/** Maximum file position */
	size_t max_offset;
	/** Block size */
	size_t blksize;
	/** Block index */
	unsigned int blkidx;
	/** Overall return status code */
	int rc;
};

/** The PXE TFTP connection */
static struct pxe_tftp_connection pxe_tftp = {
	.xfer = XFER_INIT ( &null_xfer_ops ),
};

/**
 * Close PXE TFTP connection
 *
 * @v rc		Final status code
 */
static void pxe_tftp_close ( int rc ) {
	xfer_nullify ( &pxe_tftp.xfer );
	xfer_close ( &pxe_tftp.xfer, rc );
	pxe_tftp.rc = rc;
}

/**
 * Receive new data
 *
 * @v xfer		Data transfer interface
 * @v iobuf		I/O buffer
 * @v meta		Transfer metadata
 * @ret rc		Return status code
 */
static int pxe_tftp_xfer_deliver_iob ( struct xfer_interface *xfer __unused,
				       struct io_buffer *iobuf,
				       struct xfer_metadata *meta ) {
	size_t len = iob_len ( iobuf );
	int rc = 0;

	/* Calculate new buffer position */
	if ( meta->whence != SEEK_CUR )
		pxe_tftp.offset = 0;
	pxe_tftp.offset += meta->offset;

	/* Copy data block to buffer */
	if ( len == 0 ) {
		/* No data (pure seek); treat as success */
	} else if ( pxe_tftp.offset < pxe_tftp.start ) {
		DBG ( " buffer underrun at %zx (min %zx)",
		      pxe_tftp.offset, pxe_tftp.start );
		rc = -ENOBUFS;
	} else if ( ( pxe_tftp.offset + len ) >
		    ( pxe_tftp.start + pxe_tftp.size ) ) {
		DBG ( " buffer overrun at %zx (max %zx)",
		      ( pxe_tftp.offset + len ),
		      ( pxe_tftp.start + pxe_tftp.size ) );
		rc = -ENOBUFS;
	} else {
		copy_to_user ( pxe_tftp.buffer,
			       ( pxe_tftp.offset - pxe_tftp.start ),
			       iobuf->data, len );
	}

	/* Calculate new buffer position */
	pxe_tftp.offset += len;

	/* Record maximum offset as the file size */
	if ( pxe_tftp.max_offset < pxe_tftp.offset )
		pxe_tftp.max_offset = pxe_tftp.offset;

	/* Terminate transfer on error */
	if ( rc != 0 )
		pxe_tftp_close ( rc );

	free_iob ( iobuf );
	return rc;
}

/**
 * Handle close() event
 *
 * @v xfer		Data transfer interface
 * @v rc		Reason for close
 */
static void pxe_tftp_xfer_close ( struct xfer_interface *xfer __unused,
				  int rc ) {
	pxe_tftp_close ( rc );
}

static struct xfer_interface_operations pxe_tftp_xfer_ops = {
	.close		= pxe_tftp_xfer_close,
	.vredirect	= xfer_vreopen,
	.window		= unlimited_xfer_window,
	.alloc_iob	= default_xfer_alloc_iob,
	.deliver_iob	= pxe_tftp_xfer_deliver_iob,
	.deliver_raw	= xfer_deliver_as_iob,
};

/**
 * Maximum length of a PXE TFTP URI
 *
 * The PXE TFTP API provides 128 characters for the filename; the
 * extra 128 bytes allow for the remainder of the URI.
 */
#define PXE_TFTP_URI_LEN 256

/**
 * Open PXE TFTP connection
 *
 * @v ipaddress		IP address
 * @v port		TFTP server port
 * @v filename		File name
 * @v blksize		Requested block size
 * @ret rc		Return status code
 */
static int pxe_tftp_open ( uint32_t ipaddress, unsigned int port,
			   const unsigned char *filename, size_t blksize,
			   int sizeonly ) {
	char uri_string[PXE_TFTP_URI_LEN];
	struct in_addr address;
	int rc;

	/* Intel bug-for-bug hack */
	pxe_set_cached_filename ( filename );

	/* Reset PXE TFTP connection structure */
	memset ( &pxe_tftp, 0, sizeof ( pxe_tftp ) );
	xfer_init ( &pxe_tftp.xfer, &pxe_tftp_xfer_ops, NULL );
	pxe_tftp.rc = -EINPROGRESS;

	/* Construct URI string */
	address.s_addr = ipaddress;
	if ( ! port )
		port = htons ( TFTP_PORT );
	if ( blksize < TFTP_DEFAULT_BLKSIZE )
		blksize = TFTP_DEFAULT_BLKSIZE;
	snprintf ( uri_string, sizeof ( uri_string ),
		   "tftp%s://%s:%d%s%s?blksize=%zd",
		   sizeonly ? "size" : "",
		   inet_ntoa ( address ), ntohs ( port ),
		   ( ( filename[0] == '/' ) ? "" : "/" ), filename, blksize );
	DBG ( " %s", uri_string );

	/* Open PXE TFTP connection */
	if ( ( rc = xfer_open_uri_string ( &pxe_tftp.xfer,
					   uri_string ) ) != 0 ) {
		DBG ( " could not open (%s)\n", strerror ( rc ) );
		return rc;
	}

	return 0;
}

/**
 * TFTP OPEN
 *
 * @v tftp_open				Pointer to a struct s_PXENV_TFTP_OPEN
 * @v s_PXENV_TFTP_OPEN::ServerIPAddress TFTP server IP address
 * @v s_PXENV_TFTP_OPEN::GatewayIPAddress Relay agent IP address, or 0.0.0.0
 * @v s_PXENV_TFTP_OPEN::FileName	Name of file to open
 * @v s_PXENV_TFTP_OPEN::TFTPPort	TFTP server UDP port
 * @v s_PXENV_TFTP_OPEN::PacketSize	TFTP blksize option to request
 * @ret #PXENV_EXIT_SUCCESS		File was opened
 * @ret #PXENV_EXIT_FAILURE		File was not opened
 * @ret s_PXENV_TFTP_OPEN::Status	PXE status code
 * @ret s_PXENV_TFTP_OPEN::PacketSize	Negotiated blksize
 * @err #PXENV_STATUS_TFTP_INVALID_PACKET_SIZE Requested blksize too small
 *
 * Opens a TFTP connection for downloading a file a block at a time
 * using pxenv_tftp_read().
 *
 * If s_PXENV_TFTP_OPEN::GatewayIPAddress is 0.0.0.0, normal IP
 * routing will take place.  See the relevant
 * @ref pxe_routing "implementation note" for more details.
 *
 * On x86, you must set the s_PXE::StatusCallout field to a nonzero
 * value before calling this function in protected mode.  You cannot
 * call this function with a 32-bit stack segment.  (See the relevant
 * @ref pxe_x86_pmode16 "implementation note" for more details.)
 * 
 * @note According to the PXE specification version 2.1, this call
 * "opens a file for reading/writing", though how writing is to be
 * achieved without the existence of an API call %pxenv_tftp_write()
 * is not made clear.
 *
 * @note Despite the existence of the numerous statements within the
 * PXE specification of the form "...if a TFTP/MTFTP or UDP connection
 * is active...", you cannot use pxenv_tftp_open() and
 * pxenv_tftp_read() to read a file via MTFTP; only via plain old
 * TFTP.  If you want to use MTFTP, use pxenv_tftp_read_file()
 * instead.  Astute readers will note that, since
 * pxenv_tftp_read_file() is an atomic operation from the point of
 * view of the PXE API, it is conceptually impossible to issue any
 * other PXE API call "if an MTFTP connection is active".
 */
PXENV_EXIT_t pxenv_tftp_open ( struct s_PXENV_TFTP_OPEN *tftp_open ) {
	int rc;

	DBG ( "PXENV_TFTP_OPEN" );

	/* Guard against callers that fail to close before re-opening */
	pxe_tftp_close ( 0 );

	/* Open connection */
	if ( ( rc = pxe_tftp_open ( tftp_open->ServerIPAddress,
				    tftp_open->TFTPPort,
				    tftp_open->FileName,
				    tftp_open->PacketSize,
				    0) ) != 0 ) {
		tftp_open->Status = PXENV_STATUS ( rc );
		return PXENV_EXIT_FAILURE;
	}

	/* Wait for OACK to arrive so that we have the block size */
	while ( ( ( rc = pxe_tftp.rc ) == -EINPROGRESS ) &&
		( pxe_tftp.max_offset == 0 ) ) {
		step();
	}
	pxe_tftp.blksize = xfer_window ( &pxe_tftp.xfer );
	tftp_open->PacketSize = pxe_tftp.blksize;
	DBG ( " blksize=%d", tftp_open->PacketSize );

	/* EINPROGRESS is normal; we don't wait for the whole transfer */
	if ( rc == -EINPROGRESS )
		rc = 0;

	tftp_open->Status = PXENV_STATUS ( rc );
	return ( rc ? PXENV_EXIT_FAILURE : PXENV_EXIT_SUCCESS );
}

/**
 * TFTP CLOSE
 *
 * @v tftp_close			Pointer to a struct s_PXENV_TFTP_CLOSE
 * @ret #PXENV_EXIT_SUCCESS		File was closed successfully
 * @ret #PXENV_EXIT_FAILURE		File was not closed
 * @ret s_PXENV_TFTP_CLOSE::Status	PXE status code
 * @err None				-
 *
 * Close a connection previously opened with pxenv_tftp_open().  You
 * must have previously opened a connection with pxenv_tftp_open().
 *
 * On x86, you must set the s_PXE::StatusCallout field to a nonzero
 * value before calling this function in protected mode.  You cannot
 * call this function with a 32-bit stack segment.  (See the relevant
 * @ref pxe_x86_pmode16 "implementation note" for more details.)
 */
PXENV_EXIT_t pxenv_tftp_close ( struct s_PXENV_TFTP_CLOSE *tftp_close ) {
	DBG ( "PXENV_TFTP_CLOSE" );

	pxe_tftp_close ( 0 );
	tftp_close->Status = PXENV_STATUS_SUCCESS;
	return PXENV_EXIT_SUCCESS;
}

/**
 * TFTP READ
 *
 * @v tftp_read				Pointer to a struct s_PXENV_TFTP_READ
 * @v s_PXENV_TFTP_READ::Buffer		Address of data buffer
 * @ret #PXENV_EXIT_SUCCESS		Data was read successfully
 * @ret #PXENV_EXIT_FAILURE		Data was not read
 * @ret s_PXENV_TFTP_READ::Status	PXE status code
 * @ret s_PXENV_TFTP_READ::PacketNumber	TFTP packet number
 * @ret s_PXENV_TFTP_READ::BufferSize	Length of data written into buffer
 *
 * Reads a single packet from a connection previously opened with
 * pxenv_tftp_open() into the data buffer pointed to by
 * s_PXENV_TFTP_READ::Buffer.  You must have previously opened a
 * connection with pxenv_tftp_open().  The data written into
 * s_PXENV_TFTP_READ::Buffer is just the file data; the various
 * network headers have already been removed.
 *
 * The buffer must be large enough to contain a packet of the size
 * negotiated via the s_PXENV_TFTP_OPEN::PacketSize field in the
 * pxenv_tftp_open() call.  It is worth noting that the PXE
 * specification does @b not require the caller to fill in
 * s_PXENV_TFTP_READ::BufferSize before calling pxenv_tftp_read(), so
 * the PXE stack is free to ignore whatever value the caller might
 * place there and just assume that the buffer is large enough.  That
 * said, it may be worth the caller always filling in
 * s_PXENV_TFTP_READ::BufferSize to guard against PXE stacks that
 * mistake it for an input parameter.
 *
 * The length of the TFTP data packet will be returned via
 * s_PXENV_TFTP_READ::BufferSize.  If this length is less than the
 * blksize negotiated via s_PXENV_TFTP_OPEN::PacketSize in the call to
 * pxenv_tftp_open(), this indicates that the block is the last block
 * in the file.  Note that zero is a valid length for
 * s_PXENV_TFTP_READ::BufferSize, and will occur when the length of
 * the file is a multiple of the blksize.
 *
 * The PXE specification doesn't actually state that calls to
 * pxenv_tftp_read() will return the data packets in strict sequential
 * order, though most PXE stacks will probably do so.  The sequence
 * number of the packet will be returned in
 * s_PXENV_TFTP_READ::PacketNumber.  The first packet in the file has
 * a sequence number of one, not zero.
 *
 * To guard against flawed PXE stacks, the caller should probably set
 * s_PXENV_TFTP_READ::PacketNumber to one less than the expected
 * returned value (i.e. set it to zero for the first call to
 * pxenv_tftp_read() and then re-use the returned s_PXENV_TFTP_READ
 * parameter block for subsequent calls without modifying
 * s_PXENV_TFTP_READ::PacketNumber between calls).  The caller should
 * also guard against potential problems caused by flawed
 * implementations returning the occasional duplicate packet, by
 * checking that the value returned in s_PXENV_TFTP_READ::PacketNumber
 * is as expected (i.e. one greater than that returned from the
 * previous call to pxenv_tftp_read()).
 *
 * On x86, you must set the s_PXE::StatusCallout field to a nonzero
 * value before calling this function in protected mode.  You cannot
 * call this function with a 32-bit stack segment.  (See the relevant
 * @ref pxe_x86_pmode16 "implementation note" for more details.)
 */
PXENV_EXIT_t pxenv_tftp_read ( struct s_PXENV_TFTP_READ *tftp_read ) {
	int rc;

	DBG ( "PXENV_TFTP_READ to %04x:%04x",
	      tftp_read->Buffer.segment, tftp_read->Buffer.offset );

	/* Read single block into buffer */
	pxe_tftp.buffer = real_to_user ( tftp_read->Buffer.segment,
					 tftp_read->Buffer.offset );
	pxe_tftp.size = pxe_tftp.blksize;
	pxe_tftp.start = pxe_tftp.offset;
	while ( ( ( rc = pxe_tftp.rc ) == -EINPROGRESS ) &&
		( pxe_tftp.offset == pxe_tftp.start ) )
		step();
	pxe_tftp.buffer = UNULL;
	tftp_read->BufferSize = ( pxe_tftp.offset - pxe_tftp.start );
	tftp_read->PacketNumber = ++pxe_tftp.blkidx;

	/* EINPROGRESS is normal if we haven't reached EOF yet */
	if ( rc == -EINPROGRESS )
		rc = 0;

	tftp_read->Status = PXENV_STATUS ( rc );
	return ( rc ? PXENV_EXIT_FAILURE : PXENV_EXIT_SUCCESS );
}

/**
 * TFTP/MTFTP read file
 *
 * @v tftp_read_file		     Pointer to a struct s_PXENV_TFTP_READ_FILE
 * @v s_PXENV_TFTP_READ_FILE::FileName		File name
 * @v s_PXENV_TFTP_READ_FILE::BufferSize 	Size of the receive buffer
 * @v s_PXENV_TFTP_READ_FILE::Buffer		Address of the receive buffer
 * @v s_PXENV_TFTP_READ_FILE::ServerIPAddress	TFTP server IP address
 * @v s_PXENV_TFTP_READ_FILE::GatewayIPAddress	Relay agent IP address
 * @v s_PXENV_TFTP_READ_FILE::McastIPAddress	File's multicast IP address
 * @v s_PXENV_TFTP_READ_FILE::TFTPClntPort	Client multicast UDP port
 * @v s_PXENV_TFTP_READ_FILE::TFTPSrvPort	Server multicast UDP port
 * @v s_PXENV_TFTP_READ_FILE::TFTPOpenTimeOut	Time to wait for first packet
 * @v s_PXENV_TFTP_READ_FILE::TFTPReopenDelay	MTFTP inactivity timeout
 * @ret #PXENV_EXIT_SUCCESS			File downloaded successfully
 * @ret #PXENV_EXIT_FAILURE			File not downloaded
 * @ret s_PXENV_TFTP_READ_FILE::Status		PXE status code
 * @ret s_PXENV_TFTP_READ_FILE::BufferSize	Length of downloaded file
 *
 * Downloads an entire file via either TFTP or MTFTP into the buffer
 * pointed to by s_PXENV_TFTP_READ_FILE::Buffer.
 *
 * The PXE specification does not make it clear how the caller
 * requests that MTFTP be used rather than TFTP (or vice versa).  One
 * reasonable guess is that setting
 * s_PXENV_TFTP_READ_FILE::McastIPAddress to 0.0.0.0 would cause TFTP
 * to be used instead of MTFTP, though it is conceivable that some PXE
 * stacks would interpret that as "use the DHCP-provided multicast IP
 * address" instead.  Some PXE stacks will not implement MTFTP at all,
 * and will always use TFTP.
 *
 * It is not specified whether or not
 * s_PXENV_TFTP_READ_FILE::TFTPSrvPort will be used as the TFTP server
 * port for TFTP (rather than MTFTP) downloads.  Callers should assume
 * that the only way to access a TFTP server on a non-standard port is
 * to use pxenv_tftp_open() and pxenv_tftp_read().
 *
 * If s_PXENV_TFTP_READ_FILE::GatewayIPAddress is 0.0.0.0, normal IP
 * routing will take place.  See the relevant
 * @ref pxe_routing "implementation note" for more details.
 *
 * It is interesting to note that s_PXENV_TFTP_READ_FILE::Buffer is an
 * #ADDR32_t type, i.e. nominally a flat physical address.  Some PXE
 * NBPs (e.g. NTLDR) are known to call pxenv_tftp_read_file() in real
 * mode with s_PXENV_TFTP_READ_FILE::Buffer set to an address above
 * 1MB.  This means that PXE stacks must be prepared to write to areas
 * outside base memory.  Exactly how this is to be achieved is not
 * specified, though using INT 15,87 is as close to a standard method
 * as any, and should probably be used.  Switching to protected-mode
 * in order to access high memory will fail if pxenv_tftp_read_file()
 * is called in V86 mode; it is reasonably to expect that a V86
 * monitor would intercept the relatively well-defined INT 15,87 if it
 * wants the PXE stack to be able to write to high memory.
 *
 * Things get even more interesting if pxenv_tftp_read_file() is
 * called in protected mode, because there is then absolutely no way
 * for the PXE stack to write to an absolute physical address.  You
 * can't even get around the problem by creating a special "access
 * everything" segment in the s_PXE data structure, because the
 * #SEGDESC_t descriptors are limited to 64kB in size.
 *
 * Previous versions of the PXE specification (e.g. WfM 1.1a) provide
 * a separate API call, %pxenv_tftp_read_file_pmode(), specifically to
 * work around this problem.  The s_PXENV_TFTP_READ_FILE_PMODE
 * parameter block splits s_PXENV_TFTP_READ_FILE::Buffer into
 * s_PXENV_TFTP_READ_FILE_PMODE::BufferSelector and
 * s_PXENV_TFTP_READ_FILE_PMODE::BufferOffset, i.e. it provides a
 * protected-mode segment:offset address for the data buffer.  This
 * API call is no longer present in version 2.1 of the PXE
 * specification.
 *
 * Etherboot makes the assumption that s_PXENV_TFTP_READ_FILE::Buffer
 * is an offset relative to the caller's data segment, when
 * pxenv_tftp_read_file() is called in protected mode.
 *
 * On x86, you must set the s_PXE::StatusCallout field to a nonzero
 * value before calling this function in protected mode.  You cannot
 * call this function with a 32-bit stack segment.  (See the relevant
 * @ref pxe_x86_pmode16 "implementation note" for more details.)
 *
 * @note Microsoft's NTLDR assumes that the filename passed in via
 * s_PXENV_TFTP_READ_FILE::FileName will be stored in the "file" field
 * of the stored DHCPACK packet, whence it will be returned via any
 * subsequent calls to pxenv_get_cached_info().  Though this is
 * essentially a bug in the Intel PXE implementation (not, for once,
 * in the specification!), it is a bug that Microsoft relies upon, and
 * so we implement this bug-for-bug compatibility by overwriting the
 * filename stored DHCPACK packet with the filename passed in
 * s_PXENV_TFTP_READ_FILE::FileName.
 *
 */
PXENV_EXIT_t pxenv_tftp_read_file ( struct s_PXENV_TFTP_READ_FILE
				    *tftp_read_file ) {
	int rc;

	DBG ( "PXENV_TFTP_READ_FILE to %08x+%x", tftp_read_file->Buffer,
	      tftp_read_file->BufferSize );

	/* Open TFTP file */
	if ( ( rc = pxe_tftp_open ( tftp_read_file->ServerIPAddress, 0,
				    tftp_read_file->FileName, 0, 0 ) ) != 0 ) {
		tftp_read_file->Status = PXENV_STATUS ( rc );
		return PXENV_EXIT_FAILURE;
	}

	/* Read entire file */
	pxe_tftp.buffer = phys_to_user ( tftp_read_file->Buffer );
	pxe_tftp.size = tftp_read_file->BufferSize;
	while ( ( rc = pxe_tftp.rc ) == -EINPROGRESS )
		step();
	pxe_tftp.buffer = UNULL;
	tftp_read_file->BufferSize = pxe_tftp.max_offset;

	/* Close TFTP file */
	pxe_tftp_close ( rc );

	tftp_read_file->Status = PXENV_STATUS ( rc );
	return ( rc ? PXENV_EXIT_FAILURE : PXENV_EXIT_SUCCESS );
}

/**
 * TFTP GET FILE SIZE
 *
 * @v tftp_get_fsize		     Pointer to a struct s_PXENV_TFTP_GET_FSIZE
 * @v s_PXENV_TFTP_GET_FSIZE::ServerIPAddress	TFTP server IP address
 * @v s_PXENV_TFTP_GET_FSIZE::GatewayIPAddress	Relay agent IP address
 * @v s_PXENV_TFTP_GET_FSIZE::FileName	File name
 * @ret #PXENV_EXIT_SUCCESS		File size was determined successfully
 * @ret #PXENV_EXIT_FAILURE		File size was not determined
 * @ret s_PXENV_TFTP_GET_FSIZE::Status	PXE status code
 * @ret s_PXENV_TFTP_GET_FSIZE::FileSize	File size
 *
 * Determine the size of a file on a TFTP server.  This uses the
 * "tsize" TFTP option, and so will not work with a TFTP server that
 * does not support TFTP options, or that does not support the "tsize"
 * option.
 *
 * The PXE specification states that this API call will @b not open a
 * TFTP connection for subsequent use with pxenv_tftp_read().  (This
 * is somewhat daft, since the only way to obtain the file size via
 * the "tsize" option involves issuing a TFTP open request, but that's
 * life.)
 *
 * You cannot call pxenv_tftp_get_fsize() while a TFTP or UDP
 * connection is open.
 *
 * If s_PXENV_TFTP_GET_FSIZE::GatewayIPAddress is 0.0.0.0, normal IP
 * routing will take place.  See the relevant
 * @ref pxe_routing "implementation note" for more details.
 *
 * On x86, you must set the s_PXE::StatusCallout field to a nonzero
 * value before calling this function in protected mode.  You cannot
 * call this function with a 32-bit stack segment.  (See the relevant
 * @ref pxe_x86_pmode16 "implementation note" for more details.)
 * 
 * @note There is no way to specify the TFTP server port with this API
 * call.  Though you can open a file using a non-standard TFTP server
 * port (via s_PXENV_TFTP_OPEN::TFTPPort or, potentially,
 * s_PXENV_TFTP_READ_FILE::TFTPSrvPort), you can only get the size of
 * a file from a TFTP server listening on the standard TFTP port.
 * "Consistency" is not a word in Intel's vocabulary.
 */
PXENV_EXIT_t pxenv_tftp_get_fsize ( struct s_PXENV_TFTP_GET_FSIZE
				    *tftp_get_fsize ) {
	int rc;

	DBG ( "PXENV_TFTP_GET_FSIZE" );

	/* Open TFTP file */
	if ( ( rc = pxe_tftp_open ( tftp_get_fsize->ServerIPAddress, 0,
				    tftp_get_fsize->FileName, 0, 1 ) ) != 0 ) {
		tftp_get_fsize->Status = PXENV_STATUS ( rc );
		return PXENV_EXIT_FAILURE;
	}

	/* Wait for initial seek to arrive, and record size */
	while ( ( ( rc = pxe_tftp.rc ) == -EINPROGRESS ) &&
		( pxe_tftp.max_offset == 0 ) ) {
		step();
	}
	tftp_get_fsize->FileSize = pxe_tftp.max_offset;
	DBG ( " fsize=%d", tftp_get_fsize->FileSize );

	/* EINPROGRESS is normal; we don't wait for the whole transfer */
	if ( rc == -EINPROGRESS )
		rc = 0;

	/* Close TFTP file */
	pxe_tftp_close ( rc );

	tftp_get_fsize->Status = PXENV_STATUS ( rc );
	return ( rc ? PXENV_EXIT_FAILURE : PXENV_EXIT_SUCCESS );
}