Re: [Qemu-devel] [PATCH V4 4/4] fw_cfg: insert fw_cfg file blobs via qemu cmdline

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 01, 2015 at 09:06:19AM +0200, Laszlo Ersek wrote:
> On 05/31/15 20:10, Michael S. Tsirkin wrote:
> > On Wed, Apr 29, 2015 at 11:21:53AM -0400, Gabriel L. Somlo wrote:
> >> Allow user supplied files to be inserted into the fw_cfg
> >> device before starting the guest. Since fw_cfg_add_file()
> >> already disallows duplicate fw_cfg file names, qemu will
> >> exit with an error message if the user supplies multiple
> >> blobs with the same fw_cfg file name, or if a blob name
> >> collides with a fw_cfg name programmatically added from
> >> within the QEMU source code. A warning message will be
> >> printed if the fw_cfg item name does not begin with the
> >> prefix "opt/", which is recommended for external, user
> >> provided blobs.
> >>
> >> Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
> >> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> > 
> > Would it make sense to make an illegal prefix a hard failure
> > instead?
> > If we don't, we'll be unable to add new file names without
> > fear of conflicts in the future.
> 
> We discussed this earlier. The idea was "mechanism, not policy", and
> that if a user violates the convention (not rule) / ignores the warning
> at some point, he's on his own when it breaks in the next version.
> 
> I don't feel overly strongly about it; just "mechanism, not policy"
> looks like a good tradition (well, good excuse anyway).
> 
> Thanks
> Laszlo

Most users never see warnings. We ship it, we support it.
If we don't want to support it, let's not ship it.

> >> ---
> >>  docs/specs/fw_cfg.txt | 21 +++++++++++++++++
> >>  qemu-options.hx       | 11 +++++++++
> >>  vl.c                  | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 95 insertions(+)
> >>
> >> diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
> >> index 6accd92..74351dd 100644
> >> --- a/docs/specs/fw_cfg.txt
> >> +++ b/docs/specs/fw_cfg.txt
> >> @@ -203,3 +203,24 @@ completes fully overwriting the item's data.
> >>  
> >>  NOTE: This function is deprecated, and will be completely removed
> >>  starting with QEMU v2.4.
> >> +
> >> +== Externally Provided Items ==
> >> +
> >> +As of v2.4, "file" fw_cfg items (i.e., items with selector keys above
> >> +FW_CFG_FILE_FIRST, and with a corresponding entry in the fw_cfg file
> >> +directory structure) may be inserted via the QEMU command line, using
> >> +the following syntax:
> >> +
> >> +    -fw_cfg [name=]<item_name>,file=<path>
> >> +
> >> +where <item_name> is the fw_cfg item name, and <path> is the location
> >> +on the host file system of a file containing the data to be inserted.
> >> +
> >> +NOTE: Users *SHOULD* choose item names beginning with the prefix "opt/"
> >> +when using the "-fw_cfg" command line option, to avoid conflicting with
> >> +item names used internally by QEMU. For instance:
> >> +
> >> +    -fw_cfg name=opt/my_item_name,file=./my_blob.bin
> >> +
> >> +Similarly, QEMU developers *SHOULD NOT* use item names prefixed with
> >> +"opt/" when inserting items programmatically, e.g. via fw_cfg_add_file().
> >> diff --git a/qemu-options.hx b/qemu-options.hx
> >> index 319d971..aa386b4 100644
> >> --- a/qemu-options.hx
> >> +++ b/qemu-options.hx
> >> @@ -2668,6 +2668,17 @@ STEXI
> >>  @table @option
> >>  ETEXI
> >>  
> >> +DEF("fw_cfg", HAS_ARG, QEMU_OPTION_fwcfg,
> >> +    "-fw_cfg [name=]<name>,file=<file>\n"
> >> +    "                add named fw_cfg entry from file\n",
> >> +    QEMU_ARCH_ALL)
> >> +STEXI
> >> +@item -fw_cfg [name=]@var{name},file=@var{file}
> >> +@findex -fw_cfg
> >> +Add named fw_cfg entry from file. @var{name} determines the name of
> >> +the entry in the fw_cfg file directory exposed to the guest.
> >> +ETEXI
> >> +
> >>  DEF("serial", HAS_ARG, QEMU_OPTION_serial, \
> >>      "-serial dev     redirect the serial port to char device 'dev'\n",
> >>      QEMU_ARCH_ALL)
> >> diff --git a/vl.c b/vl.c
> >> index 74c2681..b02b2d4 100644
> >> --- a/vl.c
> >> +++ b/vl.c
> >> @@ -490,6 +490,25 @@ static QemuOptsList qemu_semihosting_config_opts = {
> >>      },
> >>  };
> >>  
> >> +static QemuOptsList qemu_fw_cfg_opts = {
> >> +    .name = "fw_cfg",
> >> +    .implied_opt_name = "name",
> >> +    .head = QTAILQ_HEAD_INITIALIZER(qemu_fw_cfg_opts.head),
> >> +    .desc = {
> >> +        {
> >> +            .name = "name",
> >> +            .type = QEMU_OPT_STRING,
> >> +            .help = "Sets the fw_cfg name of the blob to be inserted",
> >> +        }, {
> >> +            .name = "file",
> >> +            .type = QEMU_OPT_STRING,
> >> +            .help = "Sets the name of the file from which\n"
> >> +                    "the fw_cfg blob will be loaded",
> >> +        },
> >> +        { /* end of list */ }
> >> +    },
> >> +};
> >> +
> >>  /**
> >>   * Get machine options
> >>   *
> >> @@ -2118,6 +2137,38 @@ char *qemu_find_file(int type, const char *name)
> >>      return NULL;
> >>  }
> >>  
> >> +static int parse_fw_cfg(QemuOpts *opts, void *opaque)
> >> +{
> >> +    gchar *buf;
> >> +    size_t size;
> >> +    const char *name, *file;
> >> +
> >> +    if (opaque == NULL) {
> >> +        error_report("fw_cfg device not available");
> >> +        return -1;
> >> +    }
> >> +    name = qemu_opt_get(opts, "name");
> >> +    file = qemu_opt_get(opts, "file");
> >> +    if (name == NULL || *name == '\0' || file == NULL || *file == '\0') {
> >> +        error_report("invalid argument value");
> >> +        return -1;
> >> +    }
> >> +    if (strlen(name) > FW_CFG_MAX_FILE_PATH - 1) {
> >> +        error_report("name too long (max. %d char)", FW_CFG_MAX_FILE_PATH - 1);
> >> +        return -1;
> >> +    }
> >> +    if (strncmp(name, "opt/", 4) != 0) {
> >> +        error_report("WARNING: externally provided fw_cfg item names "
> >> +                     "should be prefixed with \"opt/\"!");
> >> +    }
> >> +    if (!g_file_get_contents(file, &buf, &size, NULL)) {
> >> +        error_report("can't load %s", file);
> >> +        return -1;
> >> +    }
> >> +    fw_cfg_add_file((FWCfgState *)opaque, name, buf, size);
> >> +    return 0;
> >> +}
> >> +
> >>  static int device_help_func(QemuOpts *opts, void *opaque)
> >>  {
> >>      return qdev_device_help(opts);
> >> @@ -2806,6 +2857,7 @@ int main(int argc, char **argv, char **envp)
> >>      qemu_add_opts(&qemu_numa_opts);
> >>      qemu_add_opts(&qemu_icount_opts);
> >>      qemu_add_opts(&qemu_semihosting_config_opts);
> >> +    qemu_add_opts(&qemu_fw_cfg_opts);
> >>  
> >>      runstate_init();
> >>  
> >> @@ -3422,6 +3474,12 @@ int main(int argc, char **argv, char **envp)
> >>                  }
> >>                  do_smbios_option(opts);
> >>                  break;
> >> +            case QEMU_OPTION_fwcfg:
> >> +                opts = qemu_opts_parse(qemu_find_opts("fw_cfg"), optarg, 1);
> >> +                if (opts == NULL) {
> >> +                    exit(1);
> >> +                }
> >> +                break;
> >>              case QEMU_OPTION_enable_kvm:
> >>                  olist = qemu_find_opts("machine");
> >>                  qemu_opts_parse(olist, "accel=kvm", 0);
> >> @@ -4233,6 +4291,11 @@ int main(int argc, char **argv, char **envp)
> >>  
> >>      numa_post_machine_init();
> >>  
> >> +    if (qemu_opts_foreach(qemu_find_opts("fw_cfg"),
> >> +                          parse_fw_cfg, fw_cfg_find(), 1) != 0) {
> >> +        exit(1);
> >> +    }
> >> +
> >>      /* init USB devices */
> >>      if (usb_enabled()) {
> >>          if (foreach_device_config(DEV_USB, usb_parse) < 0)
> >> -- 
> >> 2.1.0
> >>