[Qemu-devel] [PATCH v3 5/5] fw_cfg: insert fw_cfg file blobs via qemu cmdline

[Gabriel L. Somlo]

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 <address@hidden>
---

I tested that object_resolve_path() always returns NULL when it can't find
a match for the given argument (i.e., rather than triggering an assert);
this means on architectures which do not create/initialize a fw_cfg object,
the call to fw_cfg_find() returns NULL.

I spent a while trying to decide whether to wrap the vl.c bits
in #ifdef CONFIG_SOFTMMU or not. Making fw_cfg_find() an always-available
static inline doesn't actually help, since I'm also calling fw_cfg_add_file()
from parse_fw_cfg(), so it's either #ifdef or no #ifdef, no point in turning
fw_cfg_find() into "static inline".

This version of the patch (without #ifdef CONFIG_SOFTMMU) actually builds
correctly, without linking errors due to missing fw_cfg symbols, on ALL
current qemu architectures (there's only *-softmmu and *-linux-user, BTW,
and the latter group doesn't actually appear to be using vl.c).

The "common-obj-y += vl.o" line in the toplevel Makefile.objs is wrapped
inside an "ifeq ($(CONFIG_SOFTMMU),y) ... endif", which would make checking
for CONFIG_SOFTMMU inside vl.c redundant anyway, so we should be good on
that front as well.

If I'm still missing anything, or something pops up that we didn't talk
about, I'd be happy to throw out a v4, just let me know.

Thanks,
   Gabriel

 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..138b9cd 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
address@hidden -fw_cfg address@hidden,address@hidden
address@hidden -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 75ec292..1fc047d 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);
@@ -4231,6 +4289,11 @@ 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