Re: [Qemu-devel] [PATCH v4 18/47] ram_debug_dump_bitmap: Dump a migration bitmap as text

[David Gibson]

On Fri, Oct 03, 2014 at 06:47:24PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> Misses out lines that are all the expected value so the output
> can be quite compact depending on the circumstance.
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  arch_init.c                   | 39 +++++++++++++++++++++++++++++++++++++++
>  include/migration/migration.h |  1 +
>  2 files changed, 40 insertions(+)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 772de36..6970733 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -769,6 +769,45 @@ static void reset_ram_globals(void)
>  
>  #define MAX_WAIT 50 /* ms, half buffered_file limit */
>  
> +/*
> + * 'expected' is the value you expect the bitmap mostly to be full
> + * of and it won't bother printing lines that are all this value
> + * if 'todump' is null the migration bitmap is dumped.
> + */
> +void ram_debug_dump_bitmap(unsigned long *todump, bool expected)
> +{
> +    int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
> +
> +    int64_t cur;
> +    int64_t linelen = 128l;

I don't think there's any point to the 'l' there.  "long" isn't
necessarily correct for an int64_t, and normal type promotion should
get this right anyway.

Assuming the user has a >128 character wide terminal seems a little
obnoxious, too.

> +    char linebuf[129];
> +
> +    if (!todump) {
> +        todump = migration_bitmap;
> +    }
> +
> +    for (cur = 0; cur < ram_pages; cur += linelen) {
> +        int64_t curb;
> +        bool found = false;
> +        /*
> +         * Last line; catch the case where the line length
> +         * is longer than remaining ram
> +         */
> +        if (cur+linelen > ram_pages) {
> +            linelen = ram_pages - cur;
> +        }
> +        for (curb = 0; curb < linelen; curb++) {
> +            bool thisbit = test_bit(cur+curb, todump);
> +            linebuf[curb] = thisbit ? '1' : '.';
> +            found |= (thisbit ^ expected);

I guess this will have the right result with the obvious encoding of a
bool, but I don't think it's conceptually correct.  It should be
logical, not bitwise operations so:
        found = found || (thisbit != expected);

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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