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Re: [Qemu-devel] [PATCH v2] fw_cfg: insert string blobs via qemu cmdline
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH v2] fw_cfg: insert string blobs via qemu cmdline |
Date: |
Mon, 28 Sep 2015 18:28:12 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 |
On 09/28/15 17:59, Gabriel L. Somlo wrote:
> Allow users to provide custom fw_cfg blobs with ascii string
> payloads specified directly on the qemu command line.
>
> Suggested-by: Jordan Justen <address@hidden>
> Suggested-by: Laszlo Ersek <address@hidden>
> Signed-off-by: Gabriel Somlo <address@hidden>
> ---
>
> new in v2:
> - clarify that NUL-terminator is NOT included in fw_cfg blob
> - replaced HAVE_OPT macro with nonempty_str() inline function
> - dropped exclamation marks from error output
> - using g_memdup() to clone content string WITHOUT terminating NUL
> - I considered simply using the content string directly,
> but explicitly bypassing the (const char *) safety check
> feels a bit dirtier than just cloning the string... :)
I diffed this against v1, and compared the changes with my v1 comments.
Reviewed-by: Laszlo Ersek <address@hidden>
Thanks!
Laszlo
>
> Thanks,
> --Gabriel
>
> docs/specs/fw_cfg.txt | 12 ++++++++++++
> qemu-options.hx | 7 ++++++-
> vl.c | 33 +++++++++++++++++++++++++++------
> 3 files changed, 45 insertions(+), 7 deletions(-)
>
> diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
> index b5f4b5d..e5552e9 100644
> --- a/docs/specs/fw_cfg.txt
> +++ b/docs/specs/fw_cfg.txt
> @@ -236,6 +236,18 @@ the following syntax:
> 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.
>
> +Small enough items may be provided directly as strings on the command
> +line, using the syntax:
> +
> + -fw_cfg [name=]<item_name>,content=<string>
> +
> +The terminating NUL character of the content <string> will NOT be
> +included as part of the fw_cfg item data, which is consistent with
> +the absence of a NUL terminator for items inserted via the file option.
> +
> +Both <item_name> and, if applicable, the content <string> are assumed
> +to consist exclusively of plain ASCII characters.
> +
> 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:
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 328404c..0b6f5bd 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2724,13 +2724,18 @@ ETEXI
>
> DEF("fw_cfg", HAS_ARG, QEMU_OPTION_fwcfg,
> "-fw_cfg [name=]<name>,file=<file>\n"
> - " add named fw_cfg entry from file\n",
> + " add named fw_cfg entry from file\n"
> + "-fw_cfg [name=]<name>,content=<str>\n"
> + " add named fw_cfg entry from string\n",
> QEMU_ARCH_ALL)
> STEXI
> @item -fw_cfg address@hidden,address@hidden
> @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.
> +
> address@hidden -fw_cfg address@hidden,address@hidden
> +Add named fw_cfg entry from string.
> ETEXI
>
> DEF("serial", HAS_ARG, QEMU_OPTION_serial, \
> diff --git a/vl.c b/vl.c
> index e211f6a..24ea82d 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -512,6 +512,10 @@ static QemuOptsList qemu_fw_cfg_opts = {
> .type = QEMU_OPT_STRING,
> .help = "Sets the name of the file from which\n"
> "the fw_cfg blob will be loaded",
> + }, {
> + .name = "content",
> + .type = QEMU_OPT_STRING,
> + .help = "Sets the content of the fw_cfg blob to be inserted",
> },
> { /* end of list */ }
> },
> @@ -2232,11 +2236,16 @@ char *qemu_find_file(int type, const char *name)
> return NULL;
> }
>
> +static inline bool nonempty_str(const char *str)
> +{
> + return str && *str;
> +}
> +
> static int parse_fw_cfg(void *opaque, QemuOpts *opts, Error **errp)
> {
> gchar *buf;
> size_t size;
> - const char *name, *file;
> + const char *name, *file, *cont;
>
> if (opaque == NULL) {
> error_report("fw_cfg device not available");
> @@ -2244,8 +2253,15 @@ static int parse_fw_cfg(void *opaque, QemuOpts *opts,
> Error **errp)
> }
> 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");
> + cont = qemu_opt_get(opts, "content");
> +
> + /* we need name and either a file or the content string */
> + if (!(nonempty_str(name) && (nonempty_str(file) || nonempty_str(cont))))
> {
> + error_report("invalid argument(s)");
> + return -1;
> + }
> + if (nonempty_str(file) && nonempty_str(cont)) {
> + error_report("file and content are mutually exclusive");
> return -1;
> }
> if (strlen(name) > FW_CFG_MAX_FILE_PATH - 1) {
> @@ -2256,9 +2272,14 @@ static int parse_fw_cfg(void *opaque, QemuOpts *opts,
> Error **errp)
> 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;
> + if (nonempty_str(cont)) {
> + size = strlen(cont); /* NUL terminator NOT included in fw_cfg blob */
> + buf = g_memdup(cont, size);
> + } else {
> + 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;
>