tftp.c

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/*
 * Copyright (C) 2006 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., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
FILE_SECBOOT ( PERMITTED );

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <byteswap.h>
#include <errno.h>
#include <assert.h>
#include <ipxe/refcnt.h>
#include <ipxe/iobuf.h>
#include <ipxe/xfer.h>
#include <ipxe/open.h>
#include <ipxe/uri.h>
#include <ipxe/tcpip.h>
#include <ipxe/retry.h>
#include <ipxe/features.h>
#include <ipxe/bitmap.h>
#include <ipxe/settings.h>
#include <ipxe/dhcp.h>
#include <ipxe/uri.h>
#include <ipxe/profile.h>
#include <ipxe/errortab.h>
#include <ipxe/tftp.h>

/** @file
 *
 * TFTP protocol
 *
 */

FEATURE ( FEATURE_PROTOCOL, "TFTP", DHCP_EB_FEATURE_TFTP, 1 );

/* TFTP-specific error codes */
#define EINVAL_BLKSIZE  __einfo_error ( EINFO_EINVAL_BLKSIZE )
#define EINFO_EINVAL_BLKSIZE __einfo_uniqify \
        ( EINFO_EINVAL, 0x01, "Invalid blksize" )
#define EINVAL_TSIZE __einfo_error ( EINFO_EINVAL_TSIZE )
#define EINFO_EINVAL_TSIZE __einfo_uniqify \
        ( EINFO_EINVAL, 0x02, "Invalid tsize" )
#define EINVAL_MC_NO_PORT __einfo_error ( EINFO_EINVAL_MC_NO_PORT )
#define EINFO_EINVAL_MC_NO_PORT __einfo_uniqify \
        ( EINFO_EINVAL, 0x03, "Missing multicast port" )
#define EINVAL_MC_NO_MC __einfo_error ( EINFO_EINVAL_MC_NO_MC )
#define EINFO_EINVAL_MC_NO_MC __einfo_uniqify \
        ( EINFO_EINVAL, 0x04, "Missing multicast mc" )
#define EINVAL_MC_INVALID_MC __einfo_error ( EINFO_EINVAL_MC_INVALID_MC )
#define EINFO_EINVAL_MC_INVALID_MC __einfo_uniqify \
        ( EINFO_EINVAL, 0x05, "Missing multicast IP" )
#define EINVAL_MC_INVALID_IP __einfo_error ( EINFO_EINVAL_MC_INVALID_IP )
#define EINFO_EINVAL_MC_INVALID_IP __einfo_uniqify \
        ( EINFO_EINVAL, 0x06, "Invalid multicast IP" )
#define EINVAL_MC_INVALID_PORT __einfo_error ( EINFO_EINVAL_MC_INVALID_PORT )
#define EINFO_EINVAL_MC_INVALID_PORT __einfo_uniqify \
        ( EINFO_EINVAL, 0x07, "Invalid multicast port" )
#define ENOENT_NOT_FOUND __einfo_error ( EINFO_ENOENT_NOT_FOUND )
#define EINFO_ENOENT_NOT_FOUND __einfo_uniqify \
        ( EINFO_ENOENT, 0x01, "Not found" )

/**
 * A TFTP request
 *
 * This data structure holds the state for an ongoing TFTP transfer.
 */
struct tftp_request {
        /** Reference count */
        struct refcnt refcnt;
        /** Data transfer interface */
        struct interface xfer;

        /** URI being fetched */
        struct uri *uri;
        /** Transport layer interface */
        struct interface socket;
        /** Multicast transport layer interface */
        struct interface mc_socket;

        /** Data block size
         *
         * This is the "blksize" option negotiated with the TFTP
         * server.  (If the TFTP server does not support TFTP options,
         * this will default to 512).
         */
        unsigned int blksize;
        /** File size
         *
         * This is the value returned in the "tsize" option from the
         * TFTP server.  If the TFTP server does not support the
         * "tsize" option, this value will be zero.
         */
        unsigned long tsize;
        
        /** Server port
         *
         * This is the port to which RRQ packets are sent.
         */
        unsigned int port;
        /** Peer address
         *
         * The peer address is determined by the first response
         * received to the TFTP RRQ.
         */
        struct sockaddr_tcpip peer;
        /** Request flags */
        unsigned int flags;
        /** MTFTP timeout count */
        unsigned int mtftp_timeouts;

        /** Block bitmap */
        struct bitmap bitmap;
        /** Maximum known length
         *
         * We don't always know the file length in advance.  In
         * particular, if the TFTP server doesn't support the tsize
         * option, or we are using MTFTP, then we don't know the file
         * length until we see the end-of-file block (which, in the
         * case of MTFTP, may not be the last block we see).
         *
         * This value is updated whenever we obtain information about
         * the file length.
         */
        size_t filesize;
        /** Retransmission timer */
        struct retry_timer timer;
};

/** TFTP request flags */
enum {
        /** Send ACK packets */
        TFTP_FL_SEND_ACK = 0x0001,
        /** Request blksize and tsize options */
        TFTP_FL_RRQ_SIZES = 0x0002,
        /** Request multicast option */
        TFTP_FL_RRQ_MULTICAST = 0x0004,
        /** Perform MTFTP recovery on timeout */
        TFTP_FL_MTFTP_RECOVERY = 0x0008,
};

/** Maximum number of MTFTP open requests before falling back to TFTP */
#define MTFTP_MAX_TIMEOUTS 3

/** Client profiler */
static struct profiler tftp_client_profiler __profiler =
        { .name = "tftp.client" };

/** Server profiler */
static struct profiler tftp_server_profiler __profiler =
        { .name = "tftp.server" };

/** Human-readable error messages */
struct errortab tftp_errors[] __errortab = {
        __einfo_errortab ( EINFO_ENOENT_NOT_FOUND ),
};

/**
 * Free TFTP request
 *
 * @v refcnt            Reference counter
 */
static void tftp_free ( struct refcnt *refcnt ) {
        struct tftp_request *tftp =
                container_of ( refcnt, struct tftp_request, refcnt );

        uri_put ( tftp->uri );
        bitmap_free ( &tftp->bitmap );
        free ( tftp );
}

/**
 * Mark TFTP request as complete
 *
 * @v tftp              TFTP connection
 * @v rc                Return status code
 */
static void tftp_done ( struct tftp_request *tftp, int rc ) {

        DBGC ( tftp, "TFTP %p finished with status %d (%s)\n",
               tftp, rc, strerror ( rc ) );

        /* Stop the retry timer */
        stop_timer ( &tftp->timer );

        /* Close all data transfer interfaces */
        intf_shutdown ( &tftp->socket, rc );
        intf_shutdown ( &tftp->mc_socket, rc );
        intf_shutdown ( &tftp->xfer, rc );
}

/**
 * Reopen TFTP socket
 *
 * @v tftp              TFTP connection
 * @ret rc              Return status code
 */
static int tftp_reopen ( struct tftp_request *tftp ) {
        struct sockaddr_tcpip server;
        int rc;

        /* Close socket */
        intf_restart ( &tftp->socket, 0 );

        /* Disable ACK sending. */
        tftp->flags &= ~TFTP_FL_SEND_ACK;

        /* Reset peer address */
        memset ( &tftp->peer, 0, sizeof ( tftp->peer ) );

        /* Open socket */
        memset ( &server, 0, sizeof ( server ) );
        server.st_port = htons ( tftp->port );
        if ( ( rc = xfer_open_named_socket ( &tftp->socket, SOCK_DGRAM,
                                             ( struct sockaddr * ) &server,
                                             tftp->uri->host, NULL ) ) != 0 ) {
                DBGC ( tftp, "TFTP %p could not open socket: %s\n",
                       tftp, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Reopen TFTP multicast socket
 *
 * @v tftp              TFTP connection
 * @v local             Local socket address
 * @ret rc              Return status code
 */
static int tftp_reopen_mc ( struct tftp_request *tftp,
                            struct sockaddr *local ) {
        int rc;

        /* Close multicast socket */
        intf_restart ( &tftp->mc_socket, 0 );

        /* Open multicast socket.  We never send via this socket, so
         * use the local address as the peer address (since the peer
         * address cannot be NULL).
         */
        if ( ( rc = xfer_open_socket ( &tftp->mc_socket, SOCK_DGRAM,
                                       local, local ) ) != 0 ) {
                DBGC ( tftp, "TFTP %p could not open multicast "
                       "socket: %s\n", tftp, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Presize TFTP receive buffers and block bitmap
 *
 * @v tftp              TFTP connection
 * @v filesize          Known minimum file size
 * @ret rc              Return status code
 */
static int tftp_presize ( struct tftp_request *tftp, size_t filesize ) {
        unsigned int num_blocks;
        int rc;

        /* Do nothing if we are already large enough */
        if ( filesize <= tftp->filesize )
                return 0;

        /* Record filesize */
        tftp->filesize = filesize;

        /* Notify recipient of file size */
        xfer_seek ( &tftp->xfer, filesize );
        xfer_seek ( &tftp->xfer, 0 );

        /* Calculate expected number of blocks.  Note that files whose
         * length is an exact multiple of the blocksize will have a
         * trailing zero-length block, which must be included.
         */
        if ( tftp->blksize == 0 )
                return -EINVAL;
        num_blocks = ( ( filesize / tftp->blksize ) + 1 );
        if ( ( rc = bitmap_resize ( &tftp->bitmap, num_blocks ) ) != 0 ) {
                DBGC ( tftp, "TFTP %p could not resize bitmap to %d blocks: "
                       "%s\n", tftp, num_blocks, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * MTFTP multicast receive address
 *
 * This is treated as a global configuration parameter.
 */
static struct sockaddr_in tftp_mtftp_socket = {
        .sin_family = AF_INET,
        .sin_addr.s_addr = htonl ( 0xefff0101 ),
        .sin_port = htons ( 3001 ),
};

/**
 * Set MTFTP multicast address
 *
 * @v address           Multicast IPv4 address
 */
void tftp_set_mtftp_address ( struct in_addr address ) {
        tftp_mtftp_socket.sin_addr = address;
}

/**
 * Set MTFTP multicast port
 *
 * @v port              Multicast port
 */
void tftp_set_mtftp_port ( unsigned int port ) {
        tftp_mtftp_socket.sin_port = htons ( port );
}

/**
 * Transmit RRQ
 *
 * @v tftp              TFTP connection
 * @ret rc              Return status code
 */
static int tftp_send_rrq ( struct tftp_request *tftp ) {
        const char *path = ( tftp->uri->path + 1 /* skip '/' */ );
        struct tftp_rrq *rrq;
        size_t len;
        struct io_buffer *iobuf;
        size_t blksize;

        DBGC ( tftp, "TFTP %p requesting \"%s\"\n", tftp, path );

        /* Allocate buffer */
        len = ( sizeof ( *rrq ) + strlen ( path ) + 1 /* NUL */
                + 5 + 1 /* "octet" + NUL */
                + 7 + 1 + 5 + 1 /* "blksize" + NUL + ddddd + NUL */
                + 5 + 1 + 1 + 1 /* "tsize" + NUL + "0" + NUL */ 
                + 9 + 1 + 1 /* "multicast" + NUL + NUL */ );
        iobuf = xfer_alloc_iob ( &tftp->socket, len );
        if ( ! iobuf )
                return -ENOMEM;

        /* Determine block size */
        blksize = xfer_window ( &tftp->xfer );
        if ( blksize > TFTP_MAX_BLKSIZE )
                blksize = TFTP_MAX_BLKSIZE;

        /* Build request */
        rrq = iob_put ( iobuf, sizeof ( *rrq ) );
        rrq->opcode = htons ( TFTP_RRQ );
        iob_put ( iobuf, snprintf ( iobuf->tail, iob_tailroom ( iobuf ),
                                    "%s%coctet", path, 0 ) + 1 );
        if ( tftp->flags & TFTP_FL_RRQ_SIZES ) {
                iob_put ( iobuf, snprintf ( iobuf->tail,
                                            iob_tailroom ( iobuf ),
                                            "blksize%c%zd%ctsize%c0",
                                            0, blksize, 0, 0 ) + 1 );
        }
        if ( tftp->flags & TFTP_FL_RRQ_MULTICAST ) {
                iob_put ( iobuf, snprintf ( iobuf->tail,
                                            iob_tailroom ( iobuf ),
                                            "multicast%c", 0 ) + 1 );
        }

        /* RRQ always goes to the address specified in the initial
         * xfer_open() call
         */
        return xfer_deliver_iob ( &tftp->socket, iobuf );
}

/**
 * Transmit ACK
 *
 * @v tftp              TFTP connection
 * @ret rc              Return status code
 */
static int tftp_send_ack ( struct tftp_request *tftp ) {
        struct tftp_ack *ack;
        struct io_buffer *iobuf;
        struct xfer_metadata meta = {
                .dest = ( struct sockaddr * ) &tftp->peer,
        };
        unsigned int block;

        /* Determine next required block number */
        block = bitmap_first_gap ( &tftp->bitmap );
        DBGC2 ( tftp, "TFTP %p sending ACK for block %d\n", tftp, block );

        /* Allocate buffer */
        iobuf = xfer_alloc_iob ( &tftp->socket, sizeof ( *ack ) );
        if ( ! iobuf )
                return -ENOMEM;

        /* Build ACK */
        ack = iob_put ( iobuf, sizeof ( *ack ) );
        ack->opcode = htons ( TFTP_ACK );
        ack->block = htons ( block );

        /* ACK always goes to the peer recorded from the RRQ response */
        return xfer_deliver ( &tftp->socket, iobuf, &meta );
}

/**
 * Transmit ERROR (Abort)
 *
 * @v tftp              TFTP connection
 * @v errcode           TFTP error code
 * @v errmsg            Error message string
 * @ret rc              Return status code
 */
static int tftp_send_error ( struct tftp_request *tftp, int errcode,
                             const char *errmsg ) {
        struct tftp_error *err;
        struct io_buffer *iobuf;
        struct xfer_metadata meta = {
                .dest = ( struct sockaddr * ) &tftp->peer,
        };
        size_t msglen;

        DBGC2 ( tftp, "TFTP %p sending ERROR %d: %s\n", tftp, errcode,
                errmsg );

        /* Allocate buffer */
        msglen = sizeof ( *err ) + strlen ( errmsg ) + 1 /* NUL */;
        iobuf = xfer_alloc_iob ( &tftp->socket, msglen );
        if ( ! iobuf )
                return -ENOMEM;

        /* Build ERROR */
        err = iob_put ( iobuf, msglen );
        err->opcode = htons ( TFTP_ERROR );
        err->errcode = htons ( errcode );
        strcpy ( err->errmsg, errmsg );

        /* ERR always goes to the peer recorded from the RRQ response */
        return xfer_deliver ( &tftp->socket, iobuf, &meta );
}

/**
 * Transmit next relevant packet
 *
 * @v tftp              TFTP connection
 * @ret rc              Return status code
 */
static int tftp_send_packet ( struct tftp_request *tftp ) {

        /* Update retransmission timer.  While name resolution takes place the
         * window is zero.  Avoid unnecessary delay after name resolution
         * completes by retrying immediately.
         */
        stop_timer ( &tftp->timer );
        if ( xfer_window ( &tftp->socket ) ) {
                start_timer ( &tftp->timer );
        } else {
                start_timer_nodelay ( &tftp->timer );
        }

        /* Send RRQ or ACK as appropriate */
        if ( ! tftp->peer.st_family ) {
                return tftp_send_rrq ( tftp );
        } else {
                if ( tftp->flags & TFTP_FL_SEND_ACK ) {
                        return tftp_send_ack ( tftp );
                } else {
                        return 0;
                }
        }
}

/**
 * Handle TFTP retransmission timer expiry
 *
 * @v timer             Retry timer
 * @v fail              Failure indicator
 */
static void tftp_timer_expired ( struct retry_timer *timer, int fail ) {
        struct tftp_request *tftp =
                container_of ( timer, struct tftp_request, timer );
        int rc;

        /* If we are doing MTFTP, attempt the various recovery strategies */
        if ( tftp->flags & TFTP_FL_MTFTP_RECOVERY ) {
                if ( tftp->peer.st_family ) {
                        /* If we have received any response from the server,
                         * try resending the RRQ to restart the download.
                         */
                        DBGC ( tftp, "TFTP %p attempting reopen\n", tftp );
                        if ( ( rc = tftp_reopen ( tftp ) ) != 0 )
                                goto err;
                } else {
                        /* Fall back to plain TFTP after several attempts */
                        tftp->mtftp_timeouts++;
                        DBGC ( tftp, "TFTP %p timeout %d waiting for MTFTP "
                               "open\n", tftp, tftp->mtftp_timeouts );

                        if ( tftp->mtftp_timeouts > MTFTP_MAX_TIMEOUTS ) {
                                DBGC ( tftp, "TFTP %p falling back to plain "
                                       "TFTP\n", tftp );
                                tftp->flags = TFTP_FL_RRQ_SIZES;

                                /* Close multicast socket */
                                intf_restart ( &tftp->mc_socket, 0 );

                                /* Reset retry timer */
                                start_timer_nodelay ( &tftp->timer );

                                /* The blocksize may change: discard
                                 * the block bitmap
                                 */
                                bitmap_free ( &tftp->bitmap );
                                memset ( &tftp->bitmap, 0,
                                         sizeof ( tftp->bitmap ) );

                                /* Reopen on standard TFTP port */
                                tftp->port = TFTP_PORT;
                                if ( ( rc = tftp_reopen ( tftp ) ) != 0 )
                                        goto err;
                        }
                }
        } else {
                /* Not doing MTFTP (or have fallen back to plain
                 * TFTP); fail as per normal.
                 */
                if ( fail ) {
                        rc = -ETIMEDOUT;
                        goto err;
                }
        }
        tftp_send_packet ( tftp );
        return;

 err:
        tftp_done ( tftp, rc );
}

/**
 * Process TFTP "blksize" option
 *
 * @v tftp              TFTP connection
 * @v value             Option value
 * @ret rc              Return status code
 */
static int tftp_process_blksize ( struct tftp_request *tftp, char *value ) {
        char *end;

        tftp->blksize = strtoul ( value, &end, 10 );
        if ( *end ) {
                DBGC ( tftp, "TFTP %p got invalid blksize \"%s\"\n",
                       tftp, value );
                return -EINVAL_BLKSIZE;
        }
        DBGC ( tftp, "TFTP %p blksize=%d\n", tftp, tftp->blksize );

        return 0;
}

/**
 * Process TFTP "tsize" option
 *
 * @v tftp              TFTP connection
 * @v value             Option value
 * @ret rc              Return status code
 */
static int tftp_process_tsize ( struct tftp_request *tftp, char *value ) {
        char *end;

        tftp->tsize = strtoul ( value, &end, 10 );
        if ( *end ) {
                DBGC ( tftp, "TFTP %p got invalid tsize \"%s\"\n",
                       tftp, value );
                return -EINVAL_TSIZE;
        }
        DBGC ( tftp, "TFTP %p tsize=%ld\n", tftp, tftp->tsize );

        return 0;
}

/**
 * Process TFTP "multicast" option
 *
 * @v tftp              TFTP connection
 * @v value             Option value
 * @ret rc              Return status code
 */
static int tftp_process_multicast ( struct tftp_request *tftp, char *value ) {
        union {
                struct sockaddr sa;
                struct sockaddr_in sin;
        } socket;
        char *addr;
        char *port;
        char *port_end;
        char *mc;
        char *mc_end;
        int rc;

        /* Split value into "addr,port,mc" fields */
        addr = value;
        port = strchr ( addr, ',' );
        if ( ! port ) {
                DBGC ( tftp, "TFTP %p multicast missing port,mc\n", tftp );
                return -EINVAL_MC_NO_PORT;
        }
        *(port++) = '\0';
        mc = strchr ( port, ',' );
        if ( ! mc ) {
                DBGC ( tftp, "TFTP %p multicast missing mc\n", tftp );
                return -EINVAL_MC_NO_MC;
        }
        *(mc++) = '\0';

        /* Parse parameters */
        if ( strtoul ( mc, &mc_end, 0 ) == 0 )
                tftp->flags &= ~TFTP_FL_SEND_ACK;
        if ( *mc_end ) {
                DBGC ( tftp, "TFTP %p multicast invalid mc %s\n", tftp, mc );
                return -EINVAL_MC_INVALID_MC;
        }
        DBGC ( tftp, "TFTP %p is%s the master client\n",
               tftp, ( ( tftp->flags & TFTP_FL_SEND_ACK ) ? "" : " not" ) );
        if ( *addr && *port ) {
                socket.sin.sin_family = AF_INET;
                if ( inet_aton ( addr, &socket.sin.sin_addr ) == 0 ) {
                        DBGC ( tftp, "TFTP %p multicast invalid IP address "
                               "%s\n", tftp, addr );
                        return -EINVAL_MC_INVALID_IP;
                }
                DBGC ( tftp, "TFTP %p multicast IP address %s\n",
                       tftp, inet_ntoa ( socket.sin.sin_addr ) );
                socket.sin.sin_port = htons ( strtoul ( port, &port_end, 0 ) );
                if ( *port_end ) {
                        DBGC ( tftp, "TFTP %p multicast invalid port %s\n",
                               tftp, port );
                        return -EINVAL_MC_INVALID_PORT;
                }
                DBGC ( tftp, "TFTP %p multicast port %d\n",
                       tftp, ntohs ( socket.sin.sin_port ) );
                if ( ( rc = tftp_reopen_mc ( tftp, &socket.sa ) ) != 0 )
                        return rc;
        }

        return 0;
}

/** A TFTP option */
struct tftp_option {
        /** Option name */
        const char *name;
        /** Option processor
         *
         * @v tftp      TFTP connection
         * @v value     Option value
         * @ret rc      Return status code
         */
        int ( * process ) ( struct tftp_request *tftp, char *value );
};

/** Recognised TFTP options */
static struct tftp_option tftp_options[] = {
        { "blksize", tftp_process_blksize },
        { "tsize", tftp_process_tsize },
        { "multicast", tftp_process_multicast },
        { NULL, NULL }
};

/**
 * Process TFTP option
 *
 * @v tftp              TFTP connection
 * @v name              Option name
 * @v value             Option value
 * @ret rc              Return status code
 */
static int tftp_process_option ( struct tftp_request *tftp,
                                 const char *name, char *value ) {
        struct tftp_option *option;

        for ( option = tftp_options ; option->name ; option++ ) {
                if ( strcasecmp ( name, option->name ) == 0 )
                        return option->process ( tftp, value );
        }

        DBGC ( tftp, "TFTP %p received unknown option \"%s\" = \"%s\"\n",
               tftp, name, value );

        /* Unknown options should be silently ignored */
        return 0;
}

/**
 * Receive OACK
 *
 * @v tftp              TFTP connection
 * @v buf               Temporary data buffer
 * @v len               Length of temporary data buffer
 * @ret rc              Return status code
 */
static int tftp_rx_oack ( struct tftp_request *tftp, void *buf, size_t len ) {
        struct tftp_oack *oack = buf;
        char *end = buf + len;
        char *name;
        char *value;
        char *next;
        int rc = 0;

        /* Sanity check */
        if ( len < sizeof ( *oack ) ) {
                DBGC ( tftp, "TFTP %p received underlength OACK packet "
                       "length %zd\n", tftp, len );
                rc = -EINVAL;
                goto done;
        }

        /* Process each option in turn */
        for ( name = oack->data ; name < end ; name = next ) {

                /* Parse option name and value
                 *
                 * We treat parsing errors as non-fatal, because there
                 * exists at least one TFTP server (IBM Tivoli PXE
                 * Server 5.1.0.3) that has been observed to send
                 * malformed OACKs containing trailing garbage bytes.
                 */
                value = ( name + strnlen ( name, ( end - name ) ) + 1 );
                if ( value > end ) {
                        DBGC ( tftp, "TFTP %p received OACK with malformed "
                               "option name:\n", tftp );
                        DBGC_HD ( tftp, oack, len );
                        break;
                }
                if ( value == end ) {
                        DBGC ( tftp, "TFTP %p received OACK missing value "
                               "for option \"%s\"\n", tftp, name );
                        DBGC_HD ( tftp, oack, len );
                        break;
                }
                next = ( value + strnlen ( value, ( end - value ) ) + 1 );
                if ( next > end ) {
                        DBGC ( tftp, "TFTP %p received OACK with malformed "
                               "value for option \"%s\":\n", tftp, name );
                        DBGC_HD ( tftp, oack, len );
                        break;
                }

                /* Process option */
                if ( ( rc = tftp_process_option ( tftp, name, value ) ) != 0 )
                        goto done;
        }

        /* Process tsize information, if available */
        if ( tftp->tsize ) {
                if ( ( rc = tftp_presize ( tftp, tftp->tsize ) ) != 0 )
                        goto done;
        }

        /* Request next data block */
        tftp_send_packet ( tftp );

 done:
        if ( rc )
                tftp_done ( tftp, rc );
        return rc;
}

/**
 * Receive DATA
 *
 * @v tftp              TFTP connection
 * @v iobuf             I/O buffer
 * @ret rc              Return status code
 *
 * Takes ownership of I/O buffer.
 */
static int tftp_rx_data ( struct tftp_request *tftp,
                          struct io_buffer *iobuf ) {
        struct tftp_data *data = iobuf->data;
        struct xfer_metadata meta;
        unsigned int block;
        off_t offset;
        size_t data_len;
        int rc;

        /* Sanity check */
        if ( iob_len ( iobuf ) < sizeof ( *data ) ) {
                DBGC ( tftp, "TFTP %p received underlength DATA packet "
                       "length %zd\n", tftp, iob_len ( iobuf ) );
                rc = -EINVAL;
                goto done;
        }

        /* Calculate block number */
        block = ( ( bitmap_first_gap ( &tftp->bitmap ) + 1 ) & ~0xffff );
        if ( data->block == 0 && block == 0 ) {
                DBGC ( tftp, "TFTP %p received data block 0\n", tftp );
                rc = -EINVAL;
                goto done;
        }
        block += ( ntohs ( data->block ) - 1 );

        /* Stop profiling server turnaround if applicable */
        if ( block )
                profile_stop ( &tftp_server_profiler );

        /* Extract data */
        offset = ( block * tftp->blksize );
        iob_pull ( iobuf, sizeof ( *data ) );
        data_len = iob_len ( iobuf );
        if ( data_len > tftp->blksize ) {
                DBGC ( tftp, "TFTP %p received overlength DATA packet "
                       "length %zd\n", tftp, data_len );
                rc = -EINVAL;
                goto done;
        }

        /* Deliver data */
        memset ( &meta, 0, sizeof ( meta ) );
        meta.flags = XFER_FL_ABS_OFFSET;
        meta.offset = offset;
        if ( ( rc = xfer_deliver ( &tftp->xfer, iob_disown ( iobuf ),
                                   &meta ) ) != 0 ) {
                DBGC ( tftp, "TFTP %p could not deliver data: %s\n",
                       tftp, strerror ( rc ) );
                goto done;
        }

        /* Ensure block bitmap is ready */
        if ( ( rc = tftp_presize ( tftp, ( offset + data_len ) ) ) != 0 )
                goto done;

        /* Mark block as received */
        bitmap_set ( &tftp->bitmap, block );

        /* Acknowledge block */
        tftp_send_packet ( tftp );

        /* Stop profiling client turnaround */
        profile_stop ( &tftp_client_profiler );

        /* Start profiling server turnaround */
        profile_start ( &tftp_server_profiler );

        /* If all blocks have been received, finish. */
        if ( bitmap_full ( &tftp->bitmap ) )
                tftp_done ( tftp, 0 );

 done:
        free_iob ( iobuf );
        if ( rc )
                tftp_done ( tftp, rc );
        return rc;
}

/**
 * Convert TFTP error code to return status code
 *
 * @v errcode           TFTP error code
 * @ret rc              Return status code
 */
static int tftp_errcode_to_rc ( unsigned int errcode ) {
        switch ( errcode ) {
        case TFTP_ERR_FILE_NOT_FOUND:   return -ENOENT_NOT_FOUND;
        case TFTP_ERR_ACCESS_DENIED:    return -EACCES;
        case TFTP_ERR_ILLEGAL_OP:       return -ENOTTY;
        default:                        return -ENOTSUP;
        }
}

/**
 * Receive ERROR
 *
 * @v tftp              TFTP connection
 * @v buf               Temporary data buffer
 * @v len               Length of temporary data buffer
 * @ret rc              Return status code
 */
static int tftp_rx_error ( struct tftp_request *tftp, void *buf, size_t len ) {
        struct tftp_error *error = buf;
        int rc;

        /* Sanity check */
        if ( len < sizeof ( *error ) ) {
                DBGC ( tftp, "TFTP %p received underlength ERROR packet "
                       "length %zd\n", tftp, len );
                return -EINVAL;
        }

        DBGC ( tftp, "TFTP %p received ERROR packet with code %d, message "
               "\"%s\"\n", tftp, ntohs ( error->errcode ), error->errmsg );
        
        /* Determine final operation result */
        rc = tftp_errcode_to_rc ( ntohs ( error->errcode ) );

        /* Close TFTP request */
        tftp_done ( tftp, rc );

        return 0;
}

/**
 * Receive new data
 *
 * @v tftp              TFTP connection
 * @v iobuf             I/O buffer
 * @v meta              Transfer metadata
 * @ret rc              Return status code
 */
static int tftp_rx ( struct tftp_request *tftp,
                     struct io_buffer *iobuf,
                     struct xfer_metadata *meta ) {
        struct sockaddr_tcpip *st_src;
        struct tftp_common *common = iobuf->data;
        size_t len = iob_len ( iobuf );
        int rc = -EINVAL;

        /* Start profiling client turnaround */
        profile_start ( &tftp_client_profiler );

        /* Sanity checks */
        if ( len < sizeof ( *common ) ) {
                DBGC ( tftp, "TFTP %p received underlength packet length "
                       "%zd\n", tftp, len );
                goto done;
        }
        if ( ! meta->src ) {
                DBGC ( tftp, "TFTP %p received packet without source port\n",
                       tftp );
                goto done;
        }

        /* Filter by TID.  Set TID on first response received */
        st_src = ( struct sockaddr_tcpip * ) meta->src;
        if ( ! tftp->peer.st_family ) {
                memcpy ( &tftp->peer, st_src, sizeof ( tftp->peer ) );
                DBGC ( tftp, "TFTP %p using remote port %d\n", tftp,
                       ntohs ( tftp->peer.st_port ) );
        } else if ( memcmp ( &tftp->peer, st_src,
                             sizeof ( tftp->peer ) ) != 0 ) {
                DBGC ( tftp, "TFTP %p received packet from wrong source (got "
                       "%d, wanted %d)\n", tftp, ntohs ( st_src->st_port ),
                       ntohs ( tftp->peer.st_port ) );
                goto done;
        }

        switch ( common->opcode ) {
        case htons ( TFTP_OACK ):
                rc = tftp_rx_oack ( tftp, iobuf->data, len );
                break;
        case htons ( TFTP_DATA ):
                rc = tftp_rx_data ( tftp, iob_disown ( iobuf ) );
                break;
        case htons ( TFTP_ERROR ):
                rc = tftp_rx_error ( tftp, iobuf->data, len );
                break;
        default:
                DBGC ( tftp, "TFTP %p received strange packet type %d\n",
                       tftp, ntohs ( common->opcode ) );
                break;
        };

 done:
        free_iob ( iobuf );
        return rc;
}

/**
 * Receive new data via socket
 *
 * @v tftp              TFTP connection
 * @v iobuf             I/O buffer
 * @v meta              Transfer metadata
 * @ret rc              Return status code
 */
static int tftp_socket_deliver ( struct tftp_request *tftp,
                                 struct io_buffer *iobuf,
                                 struct xfer_metadata *meta ) {

        /* Enable sending ACKs when we receive a unicast packet.  This
         * covers three cases:
         *
         * 1. Standard TFTP; we should always send ACKs, and will
         *    always receive a unicast packet before we need to send the
         *    first ACK.
         *
         * 2. RFC2090 multicast TFTP; the only unicast packets we will
         *    receive are the OACKs; enable sending ACKs here (before
         *    processing the OACK) and disable it when processing the
         *    multicast option if we are not the master client.
         *
         * 3. MTFTP; receiving a unicast datagram indicates that we
         *    are the "master client" and should send ACKs.
         */
        tftp->flags |= TFTP_FL_SEND_ACK;

        return tftp_rx ( tftp, iobuf, meta );
}

/** TFTP socket operations */
static struct interface_operation tftp_socket_operations[] = {
        INTF_OP ( xfer_deliver, struct tftp_request *, tftp_socket_deliver ),
};

/** TFTP socket interface descriptor */
static struct interface_descriptor tftp_socket_desc =
        INTF_DESC ( struct tftp_request, socket, tftp_socket_operations );

/** TFTP multicast socket operations */
static struct interface_operation tftp_mc_socket_operations[] = {
        INTF_OP ( xfer_deliver, struct tftp_request *, tftp_rx ),
};

/** TFTP multicast socket interface descriptor */
static struct interface_descriptor tftp_mc_socket_desc =
        INTF_DESC ( struct tftp_request, mc_socket, tftp_mc_socket_operations );

/**
 * Check flow control window
 *
 * @v tftp              TFTP connection
 * @ret len             Length of window
 */
static size_t tftp_xfer_window ( struct tftp_request *tftp ) {

        /* We abuse this data-xfer method to convey the blocksize to
         * the caller.  This really should be done using some kind of
         * stat() method, but we don't yet have the facility to do
         * that.
         */
        return tftp->blksize;
}

/**
 * Terminate download
 *
 * @v tftp              TFTP connection
 * @v rc                Reason for close
 */
static void tftp_close ( struct tftp_request *tftp, int rc ) {

        /* Abort download */
        tftp_send_error ( tftp, 0, "TFTP Aborted" );

        /* Close TFTP request */
        tftp_done ( tftp, rc );
}

/** TFTP data transfer interface operations */
static struct interface_operation tftp_xfer_operations[] = {
        INTF_OP ( xfer_window, struct tftp_request *, tftp_xfer_window ),
        INTF_OP ( intf_close, struct tftp_request *, tftp_close ),
};

/** TFTP data transfer interface descriptor */
static struct interface_descriptor tftp_xfer_desc =
        INTF_DESC ( struct tftp_request, xfer, tftp_xfer_operations );

/**
 * Initiate TFTP/TFTM/MTFTP download
 *
 * @v xfer              Data transfer interface
 * @v uri               Uniform Resource Identifier
 * @ret rc              Return status code
 */
static int tftp_core_open ( struct interface *xfer, struct uri *uri,
                            unsigned int default_port,
                            struct sockaddr *multicast,
                            unsigned int flags ) {
        struct tftp_request *tftp;
        int rc;

        /* Sanity checks */
        if ( ! uri->host )
                return -EINVAL;
        if ( ! uri->path )
                return -EINVAL;
        if ( uri->path[0] != '/' )
                return -EINVAL;

        /* Allocate and populate TFTP structure */
        tftp = zalloc ( sizeof ( *tftp ) );
        if ( ! tftp )
                return -ENOMEM;
        ref_init ( &tftp->refcnt, tftp_free );
        intf_init ( &tftp->xfer, &tftp_xfer_desc, &tftp->refcnt );
        intf_init ( &tftp->socket, &tftp_socket_desc, &tftp->refcnt );
        intf_init ( &tftp->mc_socket, &tftp_mc_socket_desc, &tftp->refcnt );
        timer_init ( &tftp->timer, tftp_timer_expired, &tftp->refcnt );
        tftp->uri = uri_get ( uri );
        tftp->blksize = TFTP_DEFAULT_BLKSIZE;
        tftp->flags = flags;

        /* Open socket */
        tftp->port = uri_port ( tftp->uri, default_port );
        if ( ( rc = tftp_reopen ( tftp ) ) != 0 )
                goto err;

        /* Open multicast socket */
        if ( multicast ) {
                if ( ( rc = tftp_reopen_mc ( tftp, multicast ) ) != 0 )
                        goto err;
        }

        /* Start timer to initiate RRQ */
        start_timer_nodelay ( &tftp->timer );

        /* Attach to parent interface, mortalise self, and return */
        intf_plug_plug ( &tftp->xfer, xfer );
        ref_put ( &tftp->refcnt );
        return 0;

 err:
        DBGC ( tftp, "TFTP %p could not create request: %s\n",
               tftp, strerror ( rc ) );
        tftp_done ( tftp, rc );
        ref_put ( &tftp->refcnt );
        return rc;
}

/**
 * Initiate TFTP download
 *
 * @v xfer              Data transfer interface
 * @v uri               Uniform Resource Identifier
 * @ret rc              Return status code
 */
static int tftp_open ( struct interface *xfer, struct uri *uri ) {
        return tftp_core_open ( xfer, uri, TFTP_PORT, NULL,
                                TFTP_FL_RRQ_SIZES );

}

/** TFTP URI opener */
struct uri_opener tftp_uri_opener __uri_opener = {
        .scheme = "tftp",
        .open   = tftp_open,
};

/**
 * Initiate TFTM download
 *
 * @v xfer              Data transfer interface
 * @v uri               Uniform Resource Identifier
 * @ret rc              Return status code
 */
static int tftm_open ( struct interface *xfer, struct uri *uri ) {
        return tftp_core_open ( xfer, uri, TFTP_PORT, NULL,
                                ( TFTP_FL_RRQ_SIZES |
                                  TFTP_FL_RRQ_MULTICAST ) );

}

/** TFTM URI opener */
struct uri_opener tftm_uri_opener __uri_opener = {
        .scheme = "tftm",
        .open   = tftm_open,
};

/**
 * Initiate MTFTP download
 *
 * @v xfer              Data transfer interface
 * @v uri               Uniform Resource Identifier
 * @ret rc              Return status code
 */
static int mtftp_open ( struct interface *xfer, struct uri *uri ) {
        return tftp_core_open ( xfer, uri, MTFTP_PORT,
                                ( struct sockaddr * ) &tftp_mtftp_socket,
                                TFTP_FL_MTFTP_RECOVERY );
}

/** MTFTP URI opener */
struct uri_opener mtftp_uri_opener __uri_opener = {
        .scheme = "mtftp",
        .open   = mtftp_open,
};

/******************************************************************************
 *
 * Settings
 *
 ******************************************************************************
 */

/**
 * Apply TFTP configuration settings
 *
 * @ret rc              Return status code
 */
static int tftp_apply_settings ( void ) {
        static struct in_addr tftp_server = { 0 };
        struct in_addr new_tftp_server;
        char uri_string[32];
        struct uri *uri;

        /* Retrieve TFTP server setting */
        fetch_ipv4_setting ( NULL, &next_server_setting, &new_tftp_server );

        /* If TFTP server setting has changed, set the current working
         * URI to match.  Do it only when the TFTP server has changed
         * to try to minimise surprises to the user, who probably
         * won't expect the CWURI to change just because they updated
         * an unrelated setting and triggered all the settings
         * applicators.
         */
        if ( new_tftp_server.s_addr &&
             ( new_tftp_server.s_addr != tftp_server.s_addr ) ) {
                DBGC ( &tftp_server, "TFTP server changed %s => ",
                       inet_ntoa ( tftp_server ) );
                DBGC ( &tftp_server, "%s\n", inet_ntoa ( new_tftp_server ) );
                snprintf ( uri_string, sizeof ( uri_string ),
                           "tftp://%s/", inet_ntoa ( new_tftp_server ) );
                uri = parse_uri ( uri_string );
                if ( ! uri )
                        return -ENOMEM;
                churi ( uri );
                uri_put ( uri );
                tftp_server = new_tftp_server;
        }

        return 0;
}

/** TFTP settings applicator */
struct settings_applicator tftp_settings_applicator __settings_applicator = {
        .apply = tftp_apply_settings,
};