Re: [Qemu-devel] [PATCH 1/1] Making pxe working in the "NAT" mode

[Anthony Liguori <anthony@codemonkey.ws>]

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Erwan Velu wrote:
> Hey folks,
> I saw the lastest qemu support pxe so I tried it using the following 
> command:
>
> qemu -hda /tmp/a.img -net nic n- user -boot n
>
> Note that now qemu support pxe mode, the mandatory -hda option is no 
> more mandatory but this is not directly linked to my patch.
> I saw qemu integrates a dhcp & a tftp server but they don't seems to 
> be configured/developped for a pxe boot process.
> Qemu says "no filename" and exits.

Hi Erwan,

I really like the idea of your patch.  Of course, the hard coding is not 
really reasonable :-)  Also, PXE is an x86-ism.  What you've really done 
is added a mechanism to publish a BOOTP name.  We do need to add a new 
option too as one may want to use -boot n without publishing a BOOTP 
filename.

Using your patch as a basis, I've written three patches.  The first one 
is the tsize negotiation fix for the TFTP server.  The second adds a 
-bootp option for specifying the location of the BOOTP image.  The third 
changes the -tftp option to take root directory.  The end result, is 
that now you can say:

qemu -hda /tmp/a.img -boot n -tftp ~/tftpboot -bootp /pxelinux.0

And you get the same results without the hard coding.  What do you think?

Regards,

Anthony Liguori

> A friend of I asked me "how do you boot using pxe in qemu when you 
> don't have a dhcp & a tftp server ?".
> So I started to look how we can do that, I modified bootp to catch the 
> field 60 of a dhcp request to find if its a pxe request or not.
> If yes, I set the filename to "/pxelinux.0", currently this is 
> harcoded, maybe you can help me to find a better way to specify a 
> bootloader.
>
> Then, I've patched the tftp server to change the default rootdir in my 
> home dir. "~/tftpboot". This is just for a Proof-of-concept, other 
> methods could be fine. We can also imagine searching in a path 
> restricted to the admin and then in the user dir. So it can give the 
> admin the ability of defining some pxe boot for all the vm of a 
> system  or in the user dir if the user wants to have a special pxe 
> boot scheme.
>
> The last patch I did on the tftp server, is to allow the tsize 
> negociation because pxelinux needs it.
>
> This patch apply to 0.9.0, once it is applied and compiled here come 
> the test procedure:
>
> create a ~/tftpboot/pxelinux.cfg directory
> copy pxelinux.0 in ~/tfptboot/
> create a pxelinux configuration file called "default" in 
> ~/tftpboot/pxelinux.cfg
>
> Et voila ;)
>
> Just call "qemu -hda /tmp/a.img -net nic n- user -boot n", it will 
> start pxelinux.
>
> I think this patch is very usefull because it give users & admin the 
> ability to use pxe inside the VM without installing the full 
> configuration (dhcp,tftp).
> This patch is mainly a proof-of-concept, this patch can be improved, 
> comments and feedback are welcome.
> _______________________________________________
> Qemu-devel mailing list
> Qemu-devel@nongnu.org
> http://lists.nongnu.org/mailman/listinfo/qemu-devel
>   


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diff -r ea5eb79ade8d slirp/bootp.c
--- a/slirp/bootp.c	Thu Feb 15 16:49:28 2007 -0600
+++ b/slirp/bootp.c	Thu Feb 15 16:49:30 2007 -0600
@@ -38,6 +38,8 @@ typedef struct {
 
 BOOTPClient bootp_clients[NB_ADDR];
 
+const char *bootp_filename;
+
 static const uint8_t rfc1533_cookie[] = { RFC1533_COOKIE };
 
 #ifdef DEBUG
@@ -168,6 +170,10 @@ static void bootp_reply(struct bootp_t *
             goto new_addr;
         }
     }
+
+    if (bootp_filename)
+        snprintf(rbp->bp_file, sizeof(rbp->bp_file), "%s", bootp_filename);
+
     dprintf("offered addr=%08x\n", ntohl(daddr.sin_addr.s_addr));
 
     saddr.sin_addr.s_addr = htonl(ntohl(special_addr.s_addr) | CTL_ALIAS);
diff -r ea5eb79ade8d vl.c
--- a/vl.c	Thu Feb 15 16:49:28 2007 -0600
+++ b/vl.c	Thu Feb 15 16:57:07 2007 -0600
@@ -6488,6 +6488,7 @@ void help(void)
            "\n"
 #ifdef CONFIG_SLIRP
            "-tftp prefix    allow tftp access to files starting with prefix [-net user]\n"
+           "-bootp file     advertise file in BOOTP replies\n"
 #ifndef _WIN32
            "-smb dir        allow SMB access to files in 'dir' [-net user]\n"
 #endif
@@ -6576,6 +6577,7 @@ enum {
 
     QEMU_OPTION_net,
     QEMU_OPTION_tftp,
+    QEMU_OPTION_bootp,
     QEMU_OPTION_smb,
     QEMU_OPTION_redir,
 
@@ -6652,6 +6654,7 @@ const QEMUOption qemu_options[] = {
     { "net", HAS_ARG, QEMU_OPTION_net},
 #ifdef CONFIG_SLIRP
     { "tftp", HAS_ARG, QEMU_OPTION_tftp },
+    { "bootp", HAS_ARG, QEMU_OPTION_bootp },
 #ifndef _WIN32
     { "smb", HAS_ARG, QEMU_OPTION_smb },
 #endif
@@ -7185,6 +7188,9 @@ int main(int argc, char **argv)
             case QEMU_OPTION_tftp:
 		tftp_prefix = optarg;
                 break;
+            case QEMU_OPTION_bootp:
+                bootp_filename = optarg;
+                break;
 #ifndef _WIN32
             case QEMU_OPTION_smb:
 		net_slirp_smb(optarg);
diff -r ea5eb79ade8d vl.h
--- a/vl.h	Thu Feb 15 16:49:28 2007 -0600
+++ b/vl.h	Thu Feb 15 16:49:30 2007 -0600
@@ -163,6 +163,7 @@ extern int no_quit;
 extern int no_quit;
 extern int semihosting_enabled;
 extern int autostart;
+extern const char *bootp_filename;
 
 #define MAX_OPTION_ROMS 16
 extern const char *option_rom[MAX_OPTION_ROMS];
diff -r ea5eb79ade8d qemu-doc.texi
--- a/qemu-doc.texi	Thu Feb 15 16:49:28 2007 -0600
+++ b/qemu-doc.texi	Thu Feb 15 16:57:23 2007 -0600
@@ -445,6 +445,16 @@ guest must be configured in binary mode 
 guest must be configured in binary mode (use the command @code{bin} of
 the Unix TFTP client). The host IP address on the guest is as usual
 10.0.2.2.
+
+@item -bootp file
+When using the user mode network stack, broadcast @var{file} as the BOOTP
+filename.  In conjunction with @option{-tftp}, this can be used to network boot
+a guest from a local directory.
+
+Example (using pxelinux):
+@example
+qemu -hda linux.img -boot n -tftp /path/to/tftp/files -bootp /pxelinux.0
+@end example
 
 @item -smb dir
 When using the user mode network stack, activate a built-in SMB

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diff -r 153828edbad3 slirp/tftp.c
--- a/slirp/tftp.c	Thu Feb 15 16:37:56 2007 -0600
+++ b/slirp/tftp.c	Thu Feb 15 21:37:26 2007 -0600
@@ -120,6 +120,45 @@ static int tftp_read_data(struct tftp_se
   return bytes_read;
 }
 
+static int tftp_send_oack(struct tftp_session *spt, 
+                          const char *key, uint32_t value,
+                          struct tftp_t *recv_tp)
+{
+    struct sockaddr_in saddr, daddr;
+    struct mbuf *m;
+    struct tftp_t *tp;
+    int n = 0;
+
+    m = m_get();
+
+    if (!m)
+	return -1;
+
+    memset(m->m_data, 0, m->m_size);
+
+    m->m_data += if_maxlinkhdr;
+    tp = (void *)m->m_data;
+    m->m_data += sizeof(struct udpiphdr);
+    
+    tp->tp_op = htons(TFTP_OACK);
+    n += sprintf(tp->x.tp_buf + n, "%s", key) + 1;
+    n += sprintf(tp->x.tp_buf + n, "%u", value) + 1;
+
+    saddr.sin_addr = recv_tp->ip.ip_dst;
+    saddr.sin_port = recv_tp->udp.uh_dport;
+    
+    daddr.sin_addr = spt->client_ip;
+    daddr.sin_port = spt->client_port;
+
+    m->m_len = sizeof(struct tftp_t) - 514 + n - 
+        sizeof(struct ip) - sizeof(struct udphdr);
+    udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
+
+    return 0;
+}
+
+
+
 static int tftp_send_error(struct tftp_session *spt, 
 			   u_int16_t errorcode, const char *msg,
 			   struct tftp_t *recv_tp)
@@ -273,6 +312,8 @@ static void tftp_handle_rrq(struct tftp_
       return;
   }
 
+  k += 6;/* skipping octet*/
+
   /* do sanity checks on the filename */
 
   if ((spt->filename[0] != '/')
@@ -297,6 +338,48 @@ static void tftp_handle_rrq(struct tftp_
       return;
   }
 
+  if (src[n - 1] != 0) {
+      tftp_send_error(spt, 2, "Access violation", tp);
+      return;
+  }
+
+  while (k < n) {
+      const char *key, *value;
+
+      key = src + k;
+      k += strlen(key) + 1;
+
+      if (k >= n) {
+	  tftp_send_error(spt, 2, "Access violation", tp);
+	  return;
+      }
+
+      value = src + k;
+      k += strlen(value) + 1;
+
+      if (strcmp(key, "tsize") == 0) {
+	  int tsize = atoi(value);
+	  struct stat stat_p;
+
+	  if (tsize == 0 && tftp_prefix) {
+	      char buffer[1024];
+	      int len;
+
+	      len = snprintf(buffer, sizeof(buffer), "%s/%s",
+			     tftp_prefix, spt->filename);
+
+	      if (stat(buffer, &stat_p) == 0)
+		  tsize = stat_p.st_size;
+	      else {
+		  tftp_send_error(spt, 1, "File not found", tp);
+		  return;
+	      }
+	  }
+
+	  tftp_send_oack(spt, "tsize", tsize, tp);
+      }
+  }
+
   tftp_send_data(spt, 1, tp);
 }
 
diff -r 153828edbad3 slirp/tftp.h
--- a/slirp/tftp.h	Thu Feb 15 16:37:56 2007 -0600
+++ b/slirp/tftp.h	Thu Feb 15 16:37:57 2007 -0600
@@ -9,6 +9,7 @@
 #define TFTP_DATA   3
 #define TFTP_ACK    4
 #define TFTP_ERROR  5
+#define TFTP_OACK   6
 
 #define TFTP_FILENAME_MAX 512
 

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diff -r 91f98dfbdc3f qemu-doc.texi
--- a/qemu-doc.texi	Thu Feb 15 21:22:02 2007 -0600
+++ b/qemu-doc.texi	Thu Feb 15 21:22:03 2007 -0600
@@ -438,13 +438,12 @@ override the default configuration (@opt
 override the default configuration (@option{-net nic -net user}) which
 is activated if no @option{-net} options are provided.
 
-@item -tftp prefix
+@item -tftp dir
 When using the user mode network stack, activate a built-in TFTP
-server. All filenames beginning with @var{prefix} can be downloaded
-from the host to the guest using a TFTP client. The TFTP client on the
-guest must be configured in binary mode (use the command @code{bin} of
-the Unix TFTP client). The host IP address on the guest is as usual
-10.0.2.2.
+server. The files in @var{dir} will be exposed as the root of a TFTP server.
+The TFTP client on the guest must be configured in binary mode (use the command
+@code{bin} of the Unix TFTP client). The host IP address on the guest is as
+usual 10.0.2.2.
 
 @item -bootp file
 When using the user mode network stack, broadcast @var{file} as the BOOTP
diff -r 91f98dfbdc3f slirp/tftp.c
--- a/slirp/tftp.c	Thu Feb 15 21:22:02 2007 -0600
+++ b/slirp/tftp.c	Thu Feb 15 21:22:03 2007 -0600
@@ -102,8 +102,15 @@ static int tftp_read_data(struct tftp_se
 {
   int fd;
   int bytes_read = 0;
-
-  fd = open(spt->filename, O_RDONLY | O_BINARY);
+  char buffer[1024];
+  int n;
+
+  n = snprintf(buffer, sizeof(buffer), "%s/%s",
+	       tftp_prefix, spt->filename);
+  if (n >= sizeof(buffer))
+    return -1;
+
+  fd = open(buffer, O_RDONLY | O_BINARY);
 
   if (fd < 0) {
     return -1;
@@ -328,8 +335,7 @@ static void tftp_handle_rrq(struct tftp_
 
   /* only allow exported prefixes */
 
-  if (!tftp_prefix
-      || (strncmp(spt->filename, tftp_prefix, strlen(tftp_prefix)) != 0)) {
+  if (!tftp_prefix) {
       tftp_send_error(spt, 2, "Access violation", tp);
       return;
   }
diff -r 91f98dfbdc3f vl.c
--- a/vl.c	Thu Feb 15 21:22:02 2007 -0600
+++ b/vl.c	Thu Feb 15 21:22:03 2007 -0600
@@ -6487,7 +6487,7 @@ void help(void)
            "                is provided, the default is '-net nic -net user'\n"
            "\n"
 #ifdef CONFIG_SLIRP
-           "-tftp prefix    allow tftp access to files starting with prefix [-net user]\n"
+           "-tftp dir       allow tftp access to files in dir [-net user]\n"
            "-bootp file     advertise file in BOOTP replies\n"
 #ifndef _WIN32
            "-smb dir        allow SMB access to files in 'dir' [-net user]\n"