diff mbox series

qemu-img.c: add help for each command

Message ID 20180908030136.844-1-programmingkidx@gmail.com (mailing list archive)
State New, archived
Headers show
Series qemu-img.c: add help for each command | expand

Commit Message

Programmingkid Sept. 8, 2018, 3:01 a.m. UTC
Add the ability for the user to display help for a certain command. 
Example: qemu-img create --help

What is printed is all the options available to this command and an example.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
---
 qemu-img.c | 767 +++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 668 insertions(+), 99 deletions(-)

Comments

Peter Maydell Sept. 8, 2018, 3:13 a.m. UTC | #1
On 8 September 2018 at 04:01, John Arbuckle <programmingkidx@gmail.com> wrote:

> +    /* print the help for this command */
> +    if (strcmp("--help", argv[optind + 1]) == 0) {
> +        if (strcmp("amend", cmdname) == 0) {
> +            help_amend();
> +        } else if (strcmp("bench", cmdname) == 0) {
> +            help_bench();
> +        } else if (strcmp("check", cmdname) == 0) {
> +            help_check();
> +        } else if (strcmp("commit", cmdname) == 0) {
> +            help_commit();
> +        } else if (strcmp("compare", cmdname) == 0) {
> +            help_compare();
> +        } else if (strcmp("convert", cmdname) == 0) {
> +            help_convert();
> +        } else if (strcmp("create", cmdname) == 0) {
> +            help_create();
> +        } else if (strcmp("dd", cmdname) == 0) {
> +            help_dd();
> +        } else if (strcmp("info", cmdname) == 0) {
> +            help_info();
> +        } else if (strcmp("map", cmdname) == 0) {
> +            help_map();
> +        } else if (strcmp("measure", cmdname) == 0) {
> +            help_measure();
> +        } else if (strcmp("snapshot", cmdname) == 0) {
> +            help_snapshot();
> +        } else if (strcmp("rebase", cmdname) == 0) {
> +            help_rebase();
> +        } else if (strcmp("resize", cmdname) == 0) {
> +            help_resize();

Any time you find yourself writing very repetitive code like
this, it's a good idea to ask yourself "is there a way to make
this data-driven?".

thanks
-- PMM
Programmingkid Sept. 8, 2018, 3:16 a.m. UTC | #2
> On Sep 7, 2018, at 11:13 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> 
> On 8 September 2018 at 04:01, John Arbuckle <programmingkidx@gmail.com> wrote:
> 
>> +    /* print the help for this command */
>> +    if (strcmp("--help", argv[optind + 1]) == 0) {
>> +        if (strcmp("amend", cmdname) == 0) {
>> +            help_amend();
>> +        } else if (strcmp("bench", cmdname) == 0) {
>> +            help_bench();
>> +        } else if (strcmp("check", cmdname) == 0) {
>> +            help_check();
>> +        } else if (strcmp("commit", cmdname) == 0) {
>> +            help_commit();
>> +        } else if (strcmp("compare", cmdname) == 0) {
>> +            help_compare();
>> +        } else if (strcmp("convert", cmdname) == 0) {
>> +            help_convert();
>> +        } else if (strcmp("create", cmdname) == 0) {
>> +            help_create();
>> +        } else if (strcmp("dd", cmdname) == 0) {
>> +            help_dd();
>> +        } else if (strcmp("info", cmdname) == 0) {
>> +            help_info();
>> +        } else if (strcmp("map", cmdname) == 0) {
>> +            help_map();
>> +        } else if (strcmp("measure", cmdname) == 0) {
>> +            help_measure();
>> +        } else if (strcmp("snapshot", cmdname) == 0) {
>> +            help_snapshot();
>> +        } else if (strcmp("rebase", cmdname) == 0) {
>> +            help_rebase();
>> +        } else if (strcmp("resize", cmdname) == 0) {
>> +            help_resize();
> 
> Any time you find yourself writing very repetitive code like
> this, it's a good idea to ask yourself "is there a way to make
> this data-driven?".
> 
> thanks
> -- PMM

Did you want me to loop thru an array of strings instead?
Kevin Wolf Sept. 10, 2018, 8:16 a.m. UTC | #3
Am 08.09.2018 um 05:16 hat Programmingkid geschrieben:
> 
> > On Sep 7, 2018, at 11:13 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> > 
> > On 8 September 2018 at 04:01, John Arbuckle <programmingkidx@gmail.com> wrote:
> > 
> >> +    /* print the help for this command */
> >> +    if (strcmp("--help", argv[optind + 1]) == 0) {
> >> +        if (strcmp("amend", cmdname) == 0) {
> >> +            help_amend();
> >> +        } else if (strcmp("bench", cmdname) == 0) {
> >> +            help_bench();
> >> +        } else if (strcmp("check", cmdname) == 0) {
> >> +            help_check();
> >> +        } else if (strcmp("commit", cmdname) == 0) {
> >> +            help_commit();
> >> +        } else if (strcmp("compare", cmdname) == 0) {
> >> +            help_compare();
> >> +        } else if (strcmp("convert", cmdname) == 0) {
> >> +            help_convert();
> >> +        } else if (strcmp("create", cmdname) == 0) {
> >> +            help_create();
> >> +        } else if (strcmp("dd", cmdname) == 0) {
> >> +            help_dd();
> >> +        } else if (strcmp("info", cmdname) == 0) {
> >> +            help_info();
> >> +        } else if (strcmp("map", cmdname) == 0) {
> >> +            help_map();
> >> +        } else if (strcmp("measure", cmdname) == 0) {
> >> +            help_measure();
> >> +        } else if (strcmp("snapshot", cmdname) == 0) {
> >> +            help_snapshot();
> >> +        } else if (strcmp("rebase", cmdname) == 0) {
> >> +            help_rebase();
> >> +        } else if (strcmp("resize", cmdname) == 0) {
> >> +            help_resize();
> > 
> > Any time you find yourself writing very repetitive code like
> > this, it's a good idea to ask yourself "is there a way to make
> > this data-driven?".
> > 
> > thanks
> > -- PMM
> 
> Did you want me to loop thru an array of strings instead?

There is already an array of all subcommands, img_cmds. You should
probably add another field there for the help text.

Also, your line wrapping (even mid-word!) is awful. I'm not sure we
really have to fill 80 characters in the output and can't simply keep
the lines a bit shorter so that 80 characters in the source are enough.

But if we do want to use the full 80 characters in the output, I'd
rather break the limit from the coding style and use longer lines in the
source coe than doing what you did.

Kevin
Programmingkid Sept. 10, 2018, 2:19 p.m. UTC | #4
> On Sep 10, 2018, at 4:16 AM, Kevin Wolf <kwolf@redhat.com> wrote:
> 
> Am 08.09.2018 um 05:16 hat Programmingkid geschrieben:
>> 
>>> On Sep 7, 2018, at 11:13 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
>>> 
>>> On 8 September 2018 at 04:01, John Arbuckle <programmingkidx@gmail.com> wrote:
>>> 
>>>> +    /* print the help for this command */
>>>> +    if (strcmp("--help", argv[optind + 1]) == 0) {
>>>> +        if (strcmp("amend", cmdname) == 0) {
>>>> +            help_amend();
>>>> +        } else if (strcmp("bench", cmdname) == 0) {
>>>> +            help_bench();
>>>> +        } else if (strcmp("check", cmdname) == 0) {
>>>> +            help_check();
>>>> +        } else if (strcmp("commit", cmdname) == 0) {
>>>> +            help_commit();
>>>> +        } else if (strcmp("compare", cmdname) == 0) {
>>>> +            help_compare();
>>>> +        } else if (strcmp("convert", cmdname) == 0) {
>>>> +            help_convert();
>>>> +        } else if (strcmp("create", cmdname) == 0) {
>>>> +            help_create();
>>>> +        } else if (strcmp("dd", cmdname) == 0) {
>>>> +            help_dd();
>>>> +        } else if (strcmp("info", cmdname) == 0) {
>>>> +            help_info();
>>>> +        } else if (strcmp("map", cmdname) == 0) {
>>>> +            help_map();
>>>> +        } else if (strcmp("measure", cmdname) == 0) {
>>>> +            help_measure();
>>>> +        } else if (strcmp("snapshot", cmdname) == 0) {
>>>> +            help_snapshot();
>>>> +        } else if (strcmp("rebase", cmdname) == 0) {
>>>> +            help_rebase();
>>>> +        } else if (strcmp("resize", cmdname) == 0) {
>>>> +            help_resize();
>>> 
>>> Any time you find yourself writing very repetitive code like
>>> this, it's a good idea to ask yourself "is there a way to make
>>> this data-driven?".
>>> 
>>> thanks
>>> -- PMM
>> 
>> Did you want me to loop thru an array of strings instead?
> 
> There is already an array of all subcommands, img_cmds. You should
> probably add another field there for the help text.

Even though I would prefer to leave the img_cmds array alone, I do
see the advantages of your suggestion. All the code that checks which
command is being used could go. I will ad a help_text field to this
array.

> Also, your line wrapping (even mid-word!) is awful. I'm not sure we
> really have to fill 80 characters in the output and can't simply keep
> the lines a bit shorter so that 80 characters in the source are enough.

Yeah it does look very unreadable like that.

> But if we do want to use the full 80 characters in the output, I'd
> rather break the limit from the coding style and use longer lines in the
> source coe than doing what you did.

Using lines longer than 80 would make the patch a lot easier to read. I will do this.

Thank you.
diff mbox series

Patch

diff --git a/qemu-img.c b/qemu-img.c
index b12f4cd..5eb38b8 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -76,11 +76,6 @@  typedef enum OutputFormat {
 /* Default to cache=writeback as data integrity is not important for qemu-img */
 #define BDRV_DEFAULT_CACHE "writeback"
 
-static void format_print(void *opaque, const char *name)
-{
-    printf(" %s", name);
-}
-
 static void QEMU_NORETURN GCC_FMT_ATTR(1, 2) error_exit(const char *fmt, ...)
 {
     va_list ap;
@@ -105,102 +100,639 @@  static void QEMU_NORETURN unrecognized_option(const char *option)
     error_exit("unrecognized option '%s'", option);
 }
 
-/* Please keep in synch with qemu-img.texi */
-static void QEMU_NORETURN help(void)
+/* Prints an overview of available help options */
+static void help(void)
 {
     const char *help_msg =
-           QEMU_IMG_VERSION
-           "usage: qemu-img [standard options] command [command options]\n"
-           "QEMU disk image utility\n"
-           "\n"
-           "    '-h', '--help'       display this help and exit\n"
-           "    '-V', '--version'    output version information and exit\n"
-           "    '-T', '--trace'      [[enable=]<pattern>][,events=<file>][,file=<file>]\n"
-           "                         specify tracing options\n"
-           "\n"
-           "Command syntax:\n"
-#define DEF(option, callback, arg_string)        \
-           "  " arg_string "\n"
-#include "qemu-img-cmds.h"
-#undef DEF
-           "\n"
-           "Command parameters:\n"
-           "  'filename' is a disk image filename\n"
-           "  'objectdef' is a QEMU user creatable object definition. See the qemu(1)\n"
-           "    manual page for a description of the object properties. The most common\n"
-           "    object type is a 'secret', which is used to supply passwords and/or\n"
-           "    encryption keys.\n"
-           "  'fmt' is the disk image format. It is guessed automatically in most cases\n"
-           "  'cache' is the cache mode used to write the output disk image, the valid\n"
-           "    options are: 'none', 'writeback' (default, except for convert), 'writethrough',\n"
-           "    'directsync' and 'unsafe' (default for convert)\n"
-           "  'src_cache' is the cache mode used to read input disk images, the valid\n"
-           "    options are the same as for the 'cache' option\n"
-           "  'size' is the disk image size in bytes. Optional suffixes\n"
-           "    'k' or 'K' (kilobyte, 1024), 'M' (megabyte, 1024k), 'G' (gigabyte, 1024M),\n"
-           "    'T' (terabyte, 1024G), 'P' (petabyte, 1024T) and 'E' (exabyte, 1024P)  are\n"
-           "    supported. 'b' is ignored.\n"
-           "  'output_filename' is the destination disk image filename\n"
-           "  'output_fmt' is the destination format\n"
-           "  'options' is a comma separated list of format specific options in a\n"
-           "    name=value format. Use -o ? for an overview of the options supported by the\n"
-           "    used format\n"
-           "  'snapshot_param' is param used for internal snapshot, format\n"
-           "    is 'snapshot.id=[ID],snapshot.name=[NAME]', or\n"
-           "    '[ID_OR_NAME]'\n"
-           "  '-c' indicates that target image must be compressed (qcow format only)\n"
-           "  '-u' allows unsafe backing chains. For rebasing, it is assumed that old and\n"
-           "       new backing file match exactly. The image doesn't need a working\n"
-           "       backing file before rebasing in this case (useful for renaming the\n"
-           "       backing file). For image creation, allow creating without attempting\n"
-           "       to open the backing file.\n"
-           "  '-h' with or without a command shows this help and lists the supported formats\n"
-           "  '-p' show progress of command (only certain commands)\n"
-           "  '-q' use Quiet mode - do not print any output (except errors)\n"
-           "  '-S' indicates the consecutive number of bytes (defaults to 4k) that must\n"
-           "       contain only zeros for qemu-img to create a sparse image during\n"
-           "       conversion. If the number of bytes is 0, the source will not be scanned for\n"
-           "       unallocated or zero sectors, and the destination image will always be\n"
-           "       fully allocated\n"
-           "  '--output' takes the format in which the output must be done (human or json)\n"
-           "  '-n' skips the target volume creation (useful if the volume is created\n"
-           "       prior to running qemu-img)\n"
-           "\n"
-           "Parameters to check subcommand:\n"
-           "  '-r' tries to repair any inconsistencies that are found during the check.\n"
-           "       '-r leaks' repairs only cluster leaks, whereas '-r all' fixes all\n"
-           "       kinds of errors, with a higher risk of choosing the wrong fix or\n"
-           "       hiding corruption that has already occurred.\n"
-           "\n"
-           "Parameters to convert subcommand:\n"
-           "  '-m' specifies how many coroutines work in parallel during the convert\n"
-           "       process (defaults to 8)\n"
-           "  '-W' allow to write to the target out of order rather than sequential\n"
-           "\n"
-           "Parameters to snapshot subcommand:\n"
-           "  'snapshot' is the name of the snapshot to create, apply or delete\n"
-           "  '-a' applies a snapshot (revert disk to saved state)\n"
-           "  '-c' creates a snapshot\n"
-           "  '-d' deletes a snapshot\n"
-           "  '-l' lists all snapshots in the given image\n"
-           "\n"
-           "Parameters to compare subcommand:\n"
-           "  '-f' first image format\n"
-           "  '-F' second image format\n"
-           "  '-s' run in Strict mode - fail on different image size or sector allocation\n"
-           "\n"
-           "Parameters to dd subcommand:\n"
-           "  'bs=BYTES' read and write up to BYTES bytes at a time "
-           "(default: 512)\n"
-           "  'count=N' copy only N input blocks\n"
-           "  'if=FILE' read from FILE\n"
-           "  'of=FILE' write to FILE\n"
-           "  'skip=N' skip N bs-sized blocks at the start of input\n";
-
-    printf("%s\nSupported formats:", help_msg);
-    bdrv_iterate_format(format_print, NULL);
-    printf("\n\n" QEMU_HELP_BOTTOM "\n");
-    exit(EXIT_SUCCESS);
+    QEMU_IMG_VERSION
+    "usage: qemu-img [standard options] command [command options]\n"
+    "QEMU disk image utility\n"
+    "\n"
+    "    '-h', '--help'       display this help and exit\n"
+    "    '-V', '--version'    output version information and exit\n"
+    "    '-T', '--trace'      [[enable=]<pattern>][,events=<file>][,file=<file>]\n"
+    "                         specify tracing options\n"
+    "\n"
+    "Command:\n"
+    "\tamend              Change options of an existing disk image\n"
+    "\tbench              Run benchmarks on a given disk image\n"
+    "\tcheck              Check the disk image for consistency or repair it\n"
+    "\tcommit             Merge the disk image into its backing file\n"
+    "\tcompare            Check if two images have the same content\n"
+    "\tconvert            Convert an image file or snapshot into another file\n"
+    "\tcreate             Create a new disk image\n"
+    "\tdd                 Copies and converts an input file into another file\n"
+    "\tinfo               Gives information about the specified image file\n"
+    "\tmap                Dump the metadata of image filename\n"
+    "\tmeasure            Calculate the file size required for a new image\n"
+    "\tsnapshot           List, apply, create or delete snapshots in a file\n"
+    "\trebase             Changes the backing file of an image file\n"
+    "\tresize             Resize an image file\n"
+    "\n\nRun 'qemu-img <command> --help' for details.\n"
+    "See <https://qemu.org/contribute/report-a-bug> for how to report bugs.\n"
+    "More information on the QEMU project at <https://qemu.org>.\n";
+    printf("%s\n", help_msg);
+}
+
+static void help_amend(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img amend [--object objectdef] [--image-opts] [-p] [-q] [-f fm"
+    "t]\n"
+    "[-t cache] -o options filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -f             The format of the image file.\n"
+    "\n"
+    "--image-opts    Treat filename as a set of image options, instead of a pla"
+    "in\n"
+    "                filename.\n"
+    "\n"
+    " -o             Used with a comma separated list of format specific option"
+    "s in a\n"
+    "                name=value format. Use \"-o help\" for an overview of the "
+    "options\n"
+    "                supported by the used format.\n"
+    "\n"
+    "--object        \'objectdef\' is a QEMU user creatable object definition. "
+    "See the\n"
+    "                qemu(1) manual page for a description of the object proper"
+    "ties.\n"
+    "                The most common object type is a \'secret\', which is used"
+    " to\n"
+    "                supply passwords and/or encryption keys.\n"
+    "\n"
+    " -p             Display progress bar. If the -p option is not used for a c"
+    "ommand\n"
+    "                that supports it, the progress is reported when the proces"
+    "s\n"
+    "                receives a \"SIGUSR1\" signal. Avoid using with the -q opt"
+    "ion.\n"
+    "\n"
+    " -q             Quiet mode - do not print any output (except errors). Avoi"
+    "d\n"
+    "                using with the -p option.\n"
+    "\n"
+    " -t             Specifies the cache mode that should be used with the\n"
+    "                destination file. Options are: none, writeback, writethrou"
+    "gh,\n"
+    "                directsync, and unsafe.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img amend -o compat=v3 -f qcow2 image.qcow2\n"
+    "    qemu-img amend --object secret,id=sec0,data=test --image-opts \\\n"
+    "    driver=luks,key-secret=sec0,file.filename=test.luks -o size=2G\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_bench(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img bench [-c count] [-d depth] [-f fmt]\n"
+    "[--flush-interval=flush_interval] [-n] [--no-drain] [-o offset]\n"
+    "[--pattern=pattern] [-q] [-s buffer_size] [-S step_size] [-t cache] [-w] ["
+    "-U]\n"
+    "filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -c                  Number of I/O requests to perform.\n"
+    "\n"
+    " -d                  Number of I/O requests done in parallel.\n"
+    "\n"
+    " -f                  The format of the image file.\n"
+    "\n"
+    " --flush-interval    How often a flush should take place.\n"
+    "\n"
+    " -n                  Use native AIO backend if possible.\n"
+    "\n"
+    " --no-drain          Issue a flush without draining the request queue firs"
+    "t.\n"
+    "\n"
+    " -o                  The starting position.\n"
+    "\n"
+    " --pattern           The byte pattern used to in write tests.\n"
+    "\n"
+    " -q                  Quiet mode - do not print any output (except errors)."
+    "\n"
+    "                     There\'s no progress bar in case both -q and -p optio"
+    "ns are\n"
+    "                     used.\n"
+    "\n"
+    " -s                  buffer_size in bytes.\n"
+    "\n"
+    " -S                  Increases current position by step_size.\n"
+    "\n"
+    " -t                  Specifies the cache mode that should be used with the"
+    "\n"
+    "                     destination file.  Options are: none, writeback,\n"
+    "                     writethrough, directsync, and unsafe.\n"
+    "\n"
+    " -w                  Perform write test.\n"
+    "\n"
+    " -U                  Open the image in shared mode, allowing other QEMU\n"
+    "                     processes to open it in write mode. This option is on"
+    "ly\n"
+    "                     allowed when opening images in read-only mode.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img bench -c 20000 -d 50000 -f qcow2 image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_check(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img check [--object objectdef] [--image-opts] [-q] [-f fmt]\n"
+    "[--output=ofmt] [-r [leaks | all]] [-T src_cache] [-U] filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -f         The format of the image file.\n"
+    "\n"
+    " -q         Use Quiet mode - do not print any output (except errors).\n"
+    "\n"
+    " -r         Tries to repair any inconsistencies that are found during the "
+    "check.\n"
+    "            \'-r leaks\' repairs only cluster leaks, whereas \'-r all\' fi"
+    "xes all\n"
+    "            kinds of errors, with a higher risk of choosing the wrong fix "
+    "or\n"
+    "            hiding corruption that has already occurred.\n"
+    "\n"
+    " -T         \'src_cache\' is the cache mode used to read input disk images"
+    ", the\n"
+    "            valid options are the same as for the \'cache\' option. Option"
+    "s are:\n"
+    "            none, writeback, writethrough, directsync, and unsafe.\n"
+    "\n"
+    " --object   \'objectdef\' is a QEMU user creatable object definition. See "
+    "the\n"
+    "            qemu(1) manual page for a description of the object properties"
+    ". The\n"
+    "            most common object type is a \'secret\', which is used to supp"
+    "ly\n"
+    "            passwords and/or encryption keys.\n"
+    "\n"
+    " --output   \'ofmt\' is \'human\' for human-readable output (default) or "
+    "\'json\' for\n"
+    "            JSON output.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img check image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_commit(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img commit [--object objectdef] [--image-opts] [-q] [-f fmt]\n"
+    "[-t cache] [-b base] [-d] [-p] filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -b            The base image or backing file.\n"
+    "\n"
+    " -d            Skip emptying filename.\n"
+    "\n"
+    " -f            The format of the image file.\n"
+    "\n"
+    " --image-opts  Treat filename as a set of image options, instead of a plai"
+    "n\n"
+    "               filename.\n"
+    "\n"
+    " --object      \'objectdef\' is a QEMU user creatable object definition. S"
+    "ee the\n"
+    "               qemu(1) manual page for a description of the object propert"
+    "ies.\n"
+    "               The most common object type is a \'secret\', which is used "
+    "to\n"
+    "               supply passwords and/or encryption keys.\n"
+    "\n"
+    " -p            Display progress bar. If the -p option is not used for a co"
+    "mmand\n"
+    "               that supports it, the progress is reported when the process"
+    "\n"
+    "               receives a \"SIGUSR1\" signal.\n"
+    "\n"
+    " -q            Quiet mode - do not print any output (except errors). There"
+    "\'s no\n"
+    "               progress bar in case both -q and -p options are used.\n"
+    "\n"
+    " -t            Specifies the cache mode that should be used with the\n"
+    "               destination file.  Options are: none, writeback, writethrou"
+    "gh,\n"
+    "               directsync, and unsafe.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img commit image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_compare(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img compare [--object objectdef] [--image-opts] [-f fmt] [-F f"
+    "mt]\n"
+    "[-T src_cache] [-p] [-q] [-s] [-U] filename1 filename2\n"
+    "\n"
+    "Command parameters:\n"
+    " -f                 First image\'s format.\n"
+    "\n"
+    " -F                 Second image\'s format.\n"
+    "\n"
+    " --image-opts       Treat filename as a set of image options, instead of a"
+    " plain\n"
+    "                    filename.\n"
+    "\n"
+    " -T                 Specifies the cache mode that should be used with the "
+    "source\n"
+    "                    file. Options are: none, writeback, writethrough,\n"
+    "                    directsync, and unsafe.\n"
+    "\n"
+    " --object           \'objectdef\' is a QEMU user creatable object definiti"
+    "on. See\n"
+    "                    the qemu(1) manual page for a description of the objec"
+    "t\n"
+    "                    properties. The most common object type is a \'secret"
+    "\', which\n"
+    "                    is used to supply passwords and/or encryption keys.\n"
+    "\n"
+    " -p                 Display progress bar. If the -p option is not used for"
+    " a\n"
+    "                    command that supports it, the progress is reported whe"
+    "n the\n"
+    "                    process receives a \"SIGUSR1\" signal.\n"
+    "\n"
+    " -q                 Quiet mode - do not print any output (except errors)."
+    "\n"
+    "                    There\'s no progress bar in case both -q and -p option"
+    "s are\n"
+    "                    used.\n"
+    "\n"
+    " -s                 Enable strict mode. Comparisons differ when image size"
+    "s\n"
+    "                    differ or if a sector is allocated in one image and no"
+    "t\n"
+    "                    allocated in the other image.\n"
+    "\n"
+    " -U                 Open the image in shared mode, allowing other QEMU\n"
+    "                    processes to open it in write mode. This option is onl"
+    "y\n"
+    "                    allowed when opening images in read-only mode.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img compare image1.qcow image2.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_convert(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img convert [--object objectdef] [--image-opts]\n"
+    "[--target-image-opts] [-U] [-c] [-p] [-q] [-n] [-f fmt] [-t cache]\n"
+    "[-T src_cache] [-O output_fmt] [-B backing_file] [-o options]\n"
+    "[-s snapshot_id_or_name] [-l snapshot_param] [-S sparse_size]\n"
+    "[-m num_coroutines] [-W] filename [filename2 [...]] output_filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -B                      Force the output image to be created as a copy on"
+    " write\n"
+    "                         image of the specified base image.\n"
+    "\n"
+    " -c                      Compress the output image file.\n"
+    "\n"
+    " -f                      The format of the image file.\n"
+    "\n"
+    " --image-opts            Indicates that the source filename parameter is t"
+    "o be\n"
+    "                         interpreted as a full option string, not a plain"
+    "\n"
+    "                         filename.\n"
+    "\n"
+    " -l                      Specifies a snapshot parameter.\n"
+    "\n"
+    " -m                      Number of parallel coroutines for the convert pro"
+    "cess\n"
+    "\n"
+    " -n                      Skip the creation of the target volume.\n"
+    "\n"
+    " -O                      Format of the output file.\n"
+    "\n"
+    " -o                      Allows for specifying options like virtual disk s"
+    "ize.\n"
+    "\n"
+    " --object                \'objectdef\' is a QEMU user creatable object def"
+    "inition.\n"
+    "                         See the qemu(1) manual page for a description of "
+    "the\n"
+    "                         object properties. The most common object type is"
+    " a\n"
+    "                         \'secret\', which is used to supply passwords and"
+    "/or\n"
+    "                         encryption keys.\n"
+    "\n"
+    " -p                      Display progress bar. If the -p option is not use"
+    "d for\n"
+    "                         a command that supports it, the progress is repor"
+    "ted\n"
+    "                         when the process receives a \"SIGUSR1\" signal.\n"
+    "\n"
+    " -q                      Quiet mode - do not print any output (except erro"
+    "rs).\n"
+    "                         There\'s no progress bar in case both -q and -p o"
+    "ptions\n"
+    "                         are used.\n"
+    "\n"
+    " -S                      The consecutive number of bytes (defaults to 4k) "
+    "that\n"
+    "                         must contain only zeros for qemu-img to create a "
+    "sparse\n"
+    "                         image during conversion.\n"
+    "\n"
+    " -s                      The name or ID of the snapshot to use.\n"
+    "\n"
+    " -T                      Specifies the cache mode that should be used with"
+    " the\n"
+    "                         source file.\n"
+    "\n"
+    " -t                      Specifies the cache mode that should be used with"
+    " the\n"
+    "                         destination file. Options are: none, writeback,\n"
+    "                         writethrough, directsync, and unsafe.\n"
+    "\n"
+    "--target-image-opts      Indicates whether the source filename includes op"
+    "tions.\n"
+    "\n"
+    " -U                      Open the image in shared mode, allowing other QEM"
+    "U\n"
+    "                         processes to open it in write mode. This option i"
+    "s only\n"
+    "                         allowed when opening images in read-only mode.\n"
+    "\n"
+    " -W                      Allow out-of-order writes to the destination. Thi"
+    "s\n"
+    "                         option improves performance, but is only recommen"
+    "ded\n"
+    "                         for preallocated devices like host devices or oth"
+    "er raw\n"
+    "                         block devices.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img convert -f raw -O qcow2 image.img image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_create(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img create [--object objectdef] [-q] [-f fmt] [-b backing_file"
+    "]\n"
+    "[-F backing_fmt] [-u] [-o options] filename [size]\n"
+    "\n"
+    "Command parameters:\n"
+    " -b             The backing file used to base the output file on.\n"
+    "\n"
+    " -f             The format of the image file.\n"
+    "\n"
+    " -F             The format of the backing file.\n"
+    "\n"
+    " -u             Create the image file even if the backing file cannot be o"
+    "pened.\n"
+    "\n"
+    " -o             Allows for specifying options like virtual disk size.\n"
+    "\n"
+    "--object        \'objectdef\' is a QEMU user creatable object definition."
+    "\n"
+    "                See the qemu(1) manual page for a description of the\n"
+    "                object properties. The most common object type is a\n"
+    "                \'secret\', which is used to supply passwords and/or\n"
+    "                encryption keys.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img create -f qcow2 image.qcow2 10G\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_dd(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img dd [-f fmt] [-O output_fmt] [bs=block_size] [count=blocks]"
+    "\n"
+    "[skip=blocks] if=input of=output\n"
+    "\n"
+    "Command parameters:\n"
+    " bs                 Size of the blocks used in reading and writing (512 by"
+    "tes is\n"
+    "                    the default).\n"
+    "\n"
+    " count              The limit to how many blocks to read.\n"
+    "\n"
+    " -f                 The format of the image file.\n"
+    "\n"
+    " if                 The input file.\n"
+    "\n"
+    " -O                 Format of the output file.\n"
+    "\n"
+    " of                 The output file.\n"
+    "\n"
+    " skip               Number of blocks to skip.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img dd if=/dev/cdrom -O raw of=cd.iso\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_info(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img info [-f fmt] [--output=ofmt] [--backing-chain] filename\n"
+    "\n"
+    "Command parameters:\n"
+    " --backing-chain            Recursively enumerate thru each disk image in "
+    "the\n"
+    "                            chain for information.\n"
+    "\n"
+    " -f                         The format of the image file.\n"
+    "\n"
+    "--output                    The output format of this command. Can be \"hu"
+    "man\" or\n"
+    "                            \"json\".\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img info image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_map(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img map [-f fmt] [--output=ofmt] filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -f                 The format of the image file.\n"
+    "\n"
+    "--output            The output format of this command. Can be \"human\" or"
+    " \"json\".\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img map image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_measure(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img measure [--output=ofmt] [-O output_fmt] [-o options] [--si"
+    "ze N ]\n"
+    "[--object objectdef] [--image-opts] [-f fmt] [-l snapshot_param]\n"
+    "filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -f                 The format of the image file.\n"
+    "\n"
+    " --image-opts       Indicates that the source filename parameter is to be"
+    "\n"
+    "                    interpreted as a full option string, not a plain\n"
+    "                    filename.\n"
+    "\n"
+    " -l                 Specifies a snapshot parameter.\n"
+    "\n"
+    " -O                 Format of the output file.\n"
+    "\n"
+    " -o                 Allows for specifying options.\n"
+    "\n"
+    " --object           \'objectdef\' is a QEMU user creatable object definiti"
+    "on. See\n"
+    "                    the qemu(1) manual page for a description of the objec"
+    "t\n"
+    "                    properties. The most common object type is a \'secret"
+    "\',\n"
+    "                    which is used to supply passwords and/or encryption ke"
+    "ys.\n"
+    "\n"
+    " --output           \'ofmt\' is \'human\' for human-readable output (defau"
+    "lt) or\n"
+    "                    \'json\' for JSON output.\n"
+    "\n"
+    " --size             If given act as if creating a new empty image file usi"
+    "ng\n"
+    "                    qemu-img create.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img measure -O qcow2 --size 5G\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_snapshot(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img snapshot [-l | -a snapshot | -c snapshot | -d snapshot ]\n"
+    "filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -a                 Applies the snapshot.\n"
+    "\n"
+    " -c                 Create a snapshot.\n"
+    "\n"
+    " -d                 Deletes a snapshot.\n"
+    "\n"
+    " -l                 Lists all snapshots\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img snapshot -l image.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_rebase(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img rebase [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b\n"
+    "backing_file [-F backing_fmt] filename\n"
+    "\n"
+    "Command parameters:\n"
+    " -b         The new backing file.\n"
+    "\n"
+    " -F         The format for the new backing file.\n"
+    "\n"
+    " -f         The format of the image file being rebased.\n"
+    "\n"
+    " -T         Specifies the cache mode that should be used with the source f"
+    "ile.\n"
+    "\n"
+    " -t         Specifies the cache mode that should be used with the destinat"
+    "ion\n"
+    "            file. Options are: none, writeback, writethrough, directsync, "
+    "and\n"
+    "            unsafe.\n"
+    "\n"
+    " -p         Display progress bar. If the -p option is not used for a comma"
+    "nd\n"
+    "            that supports it, the progress is reported when the process\n"
+    "            receives a \"SIGUSR1\" signal.\n"
+    "\n"
+    " -u         Operate in unsafe mode.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img rebase -b backing.img diff.qcow2\n"
+    "\n"
+    "\n";
+    printf("%s", msg);
+}
+
+static void help_resize(void)
+{
+    const char *msg =
+    "\n"
+    "usage: qemu-img resize [--shrink] [--preallocation=prealloc] filename\n"
+    "[+ | -] size\n"
+    "\n"
+    "Command parameters:\n"
+    " --preallocation    When growing an image, specify how the additional imag"
+    "e\n"
+    "                    area should be allocated on the host.\n"
+    "\n"
+    " --shrink           Informs qemu-img that the user acknowledges all loss o"
+    "f\n"
+    "                    data beyond the truncated image\'s end.\n"
+    "\n"
+    "Example:\n"
+    "    qemu-img resize image.qcow2 20G\n";
+    printf("%s", msg);
 }
 
 static QemuOptsList qemu_object_opts = {
@@ -4954,6 +5486,43 @@  int main(int argc, char **argv)
 
     cmdname = argv[optind];
 
+    /* print the help for this command */
+    if (strcmp("--help", argv[optind + 1]) == 0) {
+        if (strcmp("amend", cmdname) == 0) {
+            help_amend();
+        } else if (strcmp("bench", cmdname) == 0) {
+            help_bench();
+        } else if (strcmp("check", cmdname) == 0) {
+            help_check();
+        } else if (strcmp("commit", cmdname) == 0) {
+            help_commit();
+        } else if (strcmp("compare", cmdname) == 0) {
+            help_compare();
+        } else if (strcmp("convert", cmdname) == 0) {
+            help_convert();
+        } else if (strcmp("create", cmdname) == 0) {
+            help_create();
+        } else if (strcmp("dd", cmdname) == 0) {
+            help_dd();
+        } else if (strcmp("info", cmdname) == 0) {
+            help_info();
+        } else if (strcmp("map", cmdname) == 0) {
+            help_map();
+        } else if (strcmp("measure", cmdname) == 0) {
+            help_measure();
+        } else if (strcmp("snapshot", cmdname) == 0) {
+            help_snapshot();
+        } else if (strcmp("rebase", cmdname) == 0) {
+            help_rebase();
+        } else if (strcmp("resize", cmdname) == 0) {
+            help_resize();
+        } else {
+            printf("\'%s\' does not have help available for it\n\n", cmdname);
+            return -1;
+        }
+        return 0;
+    }
+
     /* reset getopt_long scanning */
     argc -= optind;
     if (argc < 1) {