github.com/system-transparency/u-root@v6.0.1-0.20190919065413-ed07a650de4c+incompatible/cmds/boot/pxeboot/pxeboot.go (about)

     1  // Copyright 2017-2018 the u-root Authors. All rights reserved
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Command pxeboot implements PXE-based booting.
     6  //
     7  // pxeboot combines a DHCP client with a TFTP/HTTP client to download files as
     8  // well as pxelinux and iPXE configuration file parsing.
     9  //
    10  // PXE-based booting requests a DHCP lease, and looks at the BootFileName and
    11  // ServerName options (which may be embedded in the original BOOTP message, or
    12  // as option codes) to find something to boot.
    13  //
    14  // This BootFileName may point to
    15  //
    16  // - an iPXE script beginning with #!ipxe
    17  //
    18  // - a pxelinux.0, in which case we will ignore the pxelinux and try to parse
    19  //   pxelinux.cfg/<files>
    20  package main
    21  
    22  import (
    23  	"context"
    24  	"flag"
    25  	"fmt"
    26  	"log"
    27  	"time"
    28  
    29  	"github.com/u-root/u-root/pkg/boot"
    30  	"github.com/u-root/u-root/pkg/dhclient"
    31  	"github.com/u-root/u-root/pkg/netboot"
    32  	"github.com/u-root/u-root/pkg/urlfetch"
    33  )
    34  
    35  var (
    36  	noLoad  = flag.Bool("no-load", false, "get DHCP response, but don't load the kernel")
    37  	dryRun  = flag.Bool("dry-run", false, "download kernel, but don't kexec it")
    38  	verbose = flag.Bool("v", false, "Verbose output")
    39  )
    40  
    41  const (
    42  	dhcpTimeout = 5 * time.Second
    43  	dhcpTries   = 3
    44  )
    45  
    46  // Netboot boots all interfaces matched by the regex in ifaceNames.
    47  func Netboot(ifaceNames string) error {
    48  	filteredIfs, err := dhclient.Interfaces(ifaceNames)
    49  	if err != nil {
    50  		return err
    51  	}
    52  
    53  	ctx, cancel := context.WithTimeout(context.Background(), (1<<dhcpTries)*dhcpTimeout)
    54  	defer cancel()
    55  
    56  	c := dhclient.Config{
    57  		Timeout: dhcpTimeout,
    58  		Retries: dhcpTries,
    59  	}
    60  	if *verbose {
    61  		c.LogLevel = dhclient.LogSummary
    62  	}
    63  	r := dhclient.SendRequests(ctx, filteredIfs, true, true, c)
    64  
    65  	for {
    66  		select {
    67  		case <-ctx.Done():
    68  			return ctx.Err()
    69  
    70  		case result, ok := <-r:
    71  			if !ok {
    72  				log.Printf("Configured all interfaces.")
    73  				return fmt.Errorf("nothing bootable found")
    74  			}
    75  			if result.Err != nil {
    76  				continue
    77  			}
    78  
    79  			if err := result.Lease.Configure(); err != nil {
    80  				log.Printf("Failed to configure lease %s: %v", result.Lease, err)
    81  				continue
    82  			}
    83  			img, err := netboot.BootImage(urlfetch.DefaultSchemes, result.Lease)
    84  			if err != nil {
    85  				log.Printf("Failed to boot lease %v: %v", result.Lease, err)
    86  				continue
    87  			}
    88  
    89  			// Cancel other DHCP requests in flight.
    90  			cancel()
    91  			log.Printf("Got configuration: %s", img)
    92  
    93  			if *noLoad {
    94  				return nil
    95  			}
    96  			if err := img.Load(*dryRun); err != nil {
    97  				return fmt.Errorf("kexec load of %v failed: %v", img, err)
    98  			}
    99  			if *dryRun {
   100  				return nil
   101  			}
   102  			if err := boot.Execute(); err != nil {
   103  				return fmt.Errorf("kexec of %v failed: %v", img, err)
   104  			}
   105  
   106  			// Kexec should either return an error or not return.
   107  			panic("unreachable")
   108  		}
   109  	}
   110  }
   111  
   112  func main() {
   113  	flag.Parse()
   114  
   115  	if err := Netboot("eth0"); err != nil {
   116  		log.Fatal(err)
   117  	}
   118  }