Re: [Qemu-devel] [PATCH v4 35/47] Page request: Add MIG_RPCOMM_REQPAGES reverse command

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Oct 03, 2014 at 06:47:41PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Add MIG_RPCOMM_REQPAGES command on Return path for the postcopy
> destination to request a page from the source.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  include/migration/migration.h |  3 ++
>  migration.c                   | 74 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 77 insertions(+)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index cdd0e56..5e0d30d 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -45,6 +45,7 @@ enum mig_rpcomm_cmd {
>      MIG_RPCOMM_INVALID = 0,  /* Must be 0 */
>      MIG_RPCOMM_SHUT,         /* sibling will not send any more RP messages */
>      MIG_RPCOMM_ACK,          /* data (seq: be32 ) */
> +    MIG_RPCOMM_REQPAGES,     /* data (start: be64, len: be64) */
>      MIG_RPCOMM_AFTERLASTVALID
>  };
>  
> @@ -250,6 +251,8 @@ void migrate_send_rp_shut(MigrationIncomingState *mis,
>                            uint32_t value);
>  void migrate_send_rp_ack(MigrationIncomingState *mis,
>                           uint32_t value);
> +void migrate_send_rp_reqpages(MigrationIncomingState *mis, const char* rbname,
> +                              ram_addr_t start, ram_addr_t len);
>  
>  
>  void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
> diff --git a/migration.c b/migration.c
> index 1731017..cfdaa52 100644
> --- a/migration.c
> +++ b/migration.c
> @@ -144,6 +144,38 @@ void migrate_send_rp_ack(MigrationIncomingState *mis,
>      migrate_send_rp_message(mis, MIG_RPCOMM_ACK, 4, (uint8_t *)&buf);
>  }
>  
> +/* Request a range of pages from the source VM at the given
> + * start address.
> + *   rbname: Name of the RAMBlock to request the page in, if NULL it's the same
> + *           as the last request (a name must have been given previously)
> + *   Start: Address offset within the RB
> + *   Len: Length in bytes required - must be a multiple of pagesize
> + */
> +void migrate_send_rp_reqpages(MigrationIncomingState *mis, const char *rbname,
> +                              ram_addr_t start, ram_addr_t len)
> +{
> +    uint8_t bufc[16+1+255]; /* start (8 byte), len (8 byte), rbname upto 256 */
> +    uint64_t *buf64 = (uint64_t *)bufc;
> +    size_t msglen = 16; /* start + len */
> +
> +    assert(!(len & 1));
> +    if (rbname) {
> +        int rbname_len = strlen(rbname);
> +        assert(rbname_len < 256);
> +
> +        len |= 1; /* Flag to say we've got a name */
> +        bufc[msglen++] = rbname_len;
> +        memcpy(bufc + msglen, rbname, rbname_len);
> +        msglen += rbname_len;
> +    }
> +
> +    buf64[0] = (uint64_t)start;
> +    buf64[0] = cpu_to_be64(buf64[0]);

I think this would be clearer as well as less verbose, as just:
	buf64[0] = cpu_to_be64(start);

> +    buf64[1] = (uint64_t)len;
> +    buf64[1] = cpu_to_be64(buf64[1]);
> +    migrate_send_rp_message(mis, MIG_RPCOMM_REQPAGES, msglen, bufc);
> +}
> +
>  void qemu_start_incoming_migration(const char *uri, Error **errp)
>  {
>      const char *p;
> @@ -784,6 +816,17 @@ static void source_return_path_bad(MigrationState *s)
>  }
>  
>  /*
> + * Process a request for pages received on the return path,
> + * We're allowed to send more than requested (e.g. to round to our page size)
> + * and we don't need to send pages that have already been sent.
> + */
> +static void migrate_handle_rp_reqpages(MigrationState *ms, const char* rbname,
> +                                       ram_addr_t start, ram_addr_t len)
> +{
> +    DPRINTF("migrate_handle_rp_reqpages: at %zx for len %zx", start, len);
> +}
> +
> +/*
>   * Handles messages sent on the return path towards the source VM
>   *
>   */
> @@ -795,6 +838,8 @@ static void *source_return_path_thread(void *opaque)
>      const int max_len = 512;
>      uint8_t buf[max_len];
>      uint32_t tmp32;
> +    uint64_t tmp64a, tmp64b;

Hrm.. calling everything "tmp*" doesn't help readability.

> +    char *tmpstr;
>      int res;
>  
>      DPRINTF("RP: %s entry", __func__);
> @@ -810,6 +855,11 @@ static void *source_return_path_thread(void *opaque)
>              expected_len = 4;
>              break;
>  
> +        case MIG_RPCOMM_REQPAGES:
> +            /* 16 byte start/len _possibly_ plus an id str */
> +            expected_len = 16 + 256;
> +            break;
> +
>          default:
>              error_report("RP: Received invalid cmd 0x%04x length 0x%04x",
>                      header_com, header_len);
> @@ -857,6 +907,30 @@ static void *source_return_path_thread(void *opaque)
>              atomic_xchg(&ms->rp_state.latest_ack, tmp32);
>              break;
>  
> +        case MIG_RPCOMM_REQPAGES:
> +            tmp64a = be64_to_cpup((uint64_t *)buf);  /* Start */
> +            tmp64b = be64_to_cpup(((uint64_t *)buf)+1); /* Len */
> +            tmpstr = NULL;
> +            if (tmp64b & 1) {
> +                tmp64b -= 1; /* Remove the flag */
> +                /* Now we expect an idstr */
> +                tmp32 = buf[16]; /* Length of the following idstr */
> +                tmpstr = (char *)&buf[17];
> +                buf[17+tmp32] = '\0';
> +                expected_len = 16+1+tmp32;
> +            } else {
> +                expected_len = 16;
> +            }
> +            if (header_len != expected_len) {
> +                error_report("RP: Received ReqPage with length %d expecting %d",
> +                        header_len, expected_len);
> +                source_return_path_bad(ms);
> +            }
> +            migrate_handle_rp_reqpages(ms, tmpstr,
> +                                          (ram_addr_t)tmp64a,
> +                                          (ram_addr_t)tmp64b);
> +            break;
> +
>          default:
>              /* This shouldn't happen because we should catch this above */
>              DPRINTF("RP: Bad header_com in dispatch");

-- 
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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