Re: [Qemu-devel] [RFC PATCH 03/56] monitor: Rewrite comment describing HMP .args_type

[Markus Armbruster]

"Dr. David Alan Gilbert" <address@hidden> writes:

> * Markus Armbruster (address@hidden) wrote:
>> Signed-off-by: Markus Armbruster <address@hidden>
>> ---
>>  monitor.c | 75 
>> +++++++++++++++++++++++++++++++++++++++------------------------
>>  1 file changed, 47 insertions(+), 28 deletions(-)
>> 
>> diff --git a/monitor.c b/monitor.c
>> index e0f8801..8b54ba1 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -85,37 +85,56 @@
>>  #endif
>>  
>>  /*
>> - * Supported types:
>> + * Command handlers (mon_cmd_t member @cmd) receive actual arguments
>> + * in a QDict, which is built by the HMP core according to mon_cmd_t
>> + * member @args_type.  It's a list of NAME:TYPE separated by comma.
>>   *
>> - * 'F'          filename
>> - * 'B'          block device name
>> - * 's'          string (accept optional quote)
>> - * 'S'          it just appends the rest of the string (accept optional 
>> quote)
>> - * 'O'          option string of the form NAME=VALUE,...
>> - *              parsed according to QemuOptsList given by its name
>> - *              Example: 'device:O' uses qemu_device_opts.
>> - *              Restriction: only lists with empty desc are supported
>> - *              TODO lift the restriction
>> - * 'i'          32 bit integer
>> - * 'l'          target long (32 or 64 bit)
>> - * 'M'          Non-negative target long (32 or 64 bit), in user mode the
>> - *              value is multiplied by 2^20 (think Mebibyte)
>> - * 'o'          octets (aka bytes)
>> - *              user mode accepts an optional E, e, P, p, T, t, G, g, M, m,
>> - *              K, k suffix, which multiplies the value by 2^60 for 
>> suffixes E
>> - *              and e, 2^50 for suffixes P and p, 2^40 for suffixes T and t,
>> - *              2^30 for suffixes G and g, 2^20 for M and m, 2^10 for K and 
>> k
>> - * 'T'          double
>> - *              user mode accepts an optional ms, us, ns suffix,
>> - *              which divides the value by 1e3, 1e6, 1e9, respectively
>> - * '/'          optional gdb-like print format (like "/10x")
>> + * TYPEs that put a string value with key NAME into the QDict:
>> + * 's'    Argument is enclosed in '"' or delimited by whitespace.  In
>> + *        the former case, escapes \n \r \\ \' and \" are recognized.
>> + * 'F'    File name, like 's' except for completion.
>> + * 'B'    BlockBackend name, like 's' except for completion.
>> + * 'S'    Argument is the remainder of the line, less leading
>> + *        whitespace.
>> +
>>   *
>> - * '?'          optional type (for all types, except '/')
>> - * '.'          other form of optional type (for 'i' and 'l')
>> - * 'b'          boolean
>> - *              user mode accepts "on" or "off"
>> - * '-'          optional parameter (eg. '-f')
>> + * TYPEs that put an int64_t value with key NAME:
>> + * 'l'    Argument is an expression (QEMU pocket calculator).
>> + * 'i'    Like 'l' except value must fit into 32 bit unsigned.
>> + * 'M'    Like 'l' except value must not be negative and is multiplied
>> + *        by 2^20 (think "mebibyte").
>>   *
>> + * TYPEs that put an uint64_t value with key NAME:
>> + * 'o'    Argument is a size (think "octets").  Without suffix the
>> + *        value is multiplied by 2^20 (mebibytes), with suffix E or e
>> + *        by 2^60 (exbibytes), with P or p by 2^50 (pebibytes), with T
>> + *        or t by 2^40 (tebibytes), with G or g by 2^30 (gibibytes),
>> + *        with M or m by 2^10 (mebibytes), with K or k by 2^10
>> + *        (kibibytes).
>
> 'o' is messy.  It using qemu_strtosz_MiB which uses a 'double' intermediate
> so I fear it can round.

It does, but only when you have more than 53 significant bits.

>                          It also has a note it can't take all f's due to
> an overflow from the conversion.

Correct, because values between 0xfffffffffffffc00 and 2^64-1 round up
to 2^64.

If it bothers you, feel free to explore the following: feed the string
both to strtod() and to strtoll().  Whichever eats more characters wins.

This patch is of course just about better documenting what we have.  I
was starting to type something like "repeating the (complex) contract of
qemu_strtosz_MiB() here isn't so hot, let's include it by reference
instead", but then I looked it up.  Pffft.

>                                    Two things not mentioned are that
> it also takes hex (as explicit 0x) and that it also does 'b' as a suffix
> to multiply by 1.  Those two combine in bad ways - i.e. 0x1b is 27MB,
> 1b is 1 byte (same for 'e').  These are probably OK except if you were
> to start replacing 'l' by 'o' because you really wanted 64bit addresses
> say.

I guess the sanest solution is not to recognize suffixes when the number
is hexadecimal.

> (I also wouldn't bother expanding the size names and powers).

I erred on the side of tedious clarity.  Feel free to suggest something
you like better.

>> + *
>> + * TYPEs that put a double value with key NAME:
>> + * 'T'    Argument is a time in seconds.  With optional ms, us, ns
>> + *        suffix, the value divided by 1e3, 1e6, 1e9 respectively.
>> + *
>> + * TYPEs that put a bool value with key NAME:
>> + * 'b'    Argument is either "on" (true) or "off" (false).
>> + * '-' CHAR
>> + *        Argument is either "-CHAR" (true) or absent (false).
>
> I found the previous description clearer.

What I don't like about the previous description: it defines by example.
Examples are great, but they are for illustrating a definition, they
can't really replace one.

>> + * TYPEs that put multiple values:
>> + * 'O'    Option string of the form NAME=VALUE,... parsed according to
>> + *        the QemuOptsList given by its name.
>> + *        Example: 'device:O' uses qemu_device_opts.
>> + *        Restriction: only lists with empty desc are supported.
>> + *        Puts all the NAME=VALUE.
>> + * '/'    Gdb-like print format (like "/10x"), always optional.
>> + *        Puts keys "count", "format", "size", all int.
>> + *
>> + * Modifier character following the type string:
>> + * '?'    Argument is optional, nothing is put when it is absent
>> + *        (all types except 'O', '/', 'b').
>> + * '.'    Argument is optional, must be preceded by '.' if present
>> + *        (only types 'i', 'l', 'M')
>
> That's obscure; I can only see one use of it in ioport_read and that's
> extra-special!

Extra-special baroque!  Took me a while to figure out WTF it does :)

>>   */
>>  
>>  typedef struct mon_cmd_t {
>> -- 
>> 2.7.5

Thanks!