Re: [Qemu-devel] [PATCH v1 08/22] migration: convert post-copy to use QIOChannelBuffer

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrange (berrange@redhat.com) wrote:
> The post-copy code does some I/O to/from an intermediate
> in-memory buffer rather than direct to the underlying
> I/O channel. Switch this code to use QIOChannelBuffer
> instead of QEMUSizedBuffer.
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  docs/migration.txt      |  4 ++--
>  include/sysemu/sysemu.h |  2 +-
>  migration/migration.c   | 15 +++++++--------
>  migration/savevm.c      | 41 +++++++++++++----------------------------
>  4 files changed, 23 insertions(+), 39 deletions(-)
> 
> diff --git a/docs/migration.txt b/docs/migration.txt
> index fda8d61..11703de 100644
> --- a/docs/migration.txt
> +++ b/docs/migration.txt
> @@ -403,8 +403,8 @@ listen thread:                     --- page -- page -- page -- page -- page --
>  
>  On receipt of CMD_PACKAGED (1)
>     All the data associated with the package - the ( ... ) section in the
> -diagram - is read into memory (into a QEMUSizedBuffer), and the main thread
> -recurses into qemu_loadvm_state_main to process the contents of the package (2)
> +diagram - is read into memory, and the main thread recurses into
> +qemu_loadvm_state_main to process the contents of the package (2)
>  which contains commands (3,6) and devices (4...)
>  
>  On receipt of 'postcopy listen' - 3 -(i.e. the 1st command in the package)
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index 3bb8897..0f59912 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -120,7 +120,7 @@ void qemu_savevm_command_send(QEMUFile *f, enum qemu_vm_cmd command,
>                                uint16_t len, uint8_t *data);
>  void qemu_savevm_send_ping(QEMUFile *f, uint32_t value);
>  void qemu_savevm_send_open_return_path(QEMUFile *f);
> -int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb);
> +int qemu_savevm_send_packaged(QEMUFile *f, const char *buf, size_t len);
>  void qemu_savevm_send_postcopy_advise(QEMUFile *f);
>  void qemu_savevm_send_postcopy_listen(QEMUFile *f);
>  void qemu_savevm_send_postcopy_run(QEMUFile *f);
> diff --git a/migration/migration.c b/migration/migration.c
> index 715f069..e921b20 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -33,6 +33,7 @@
>  #include "qom/cpu.h"
>  #include "exec/memory.h"
>  #include "exec/address-spaces.h"
> +#include "io/channel-buffer.h"
>  
>  #define MAX_THROTTLE  (32 << 20)      /* Migration transfer speed throttling */
>  
> @@ -1401,7 +1402,8 @@ static int await_return_path_close_on_source(MigrationState *ms)
>  static int postcopy_start(MigrationState *ms, bool *old_vm_running)
>  {
>      int ret;
> -    const QEMUSizedBuffer *qsb;
> +    QIOChannelBuffer *bioc;
> +    QEMUFile *fb;
>      int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
>      migrate_set_state(ms, MIGRATION_STATUS_ACTIVE,
>                        MIGRATION_STATUS_POSTCOPY_ACTIVE);
> @@ -1456,11 +1458,9 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
>       * So we wrap the device state up in a package with a length at the start;
>       * to do this we use a qemu_buf to hold the whole of the device state.
>       */
> -    QEMUFile *fb = qemu_bufopen("w", NULL);
> -    if (!fb) {
> -        error_report("Failed to create buffered file");
> -        goto fail;
> -    }
> +    bioc = qio_channel_buffer_new(4096);
> +    fb = qemu_fopen_channel_input(QIO_CHANNEL(bioc));

Why is that _input ?
Also, what's your naming converntion; my 'qsb' was just an
abbreviation of (Q)EMU(S)ized(B)uffer;  what's a bioc?

> +    object_unref(OBJECT(bioc));
>  
>      /*
>       * Make sure the receiver can get incoming pages before we send the rest
> @@ -1474,10 +1474,9 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
>      qemu_savevm_send_postcopy_run(fb);
>  
>      /* <><> end of stuff going into the package */
> -    qsb = qemu_buf_get(fb);
>  
>      /* Now send that blob */
> -    if (qemu_savevm_send_packaged(ms->file, qsb)) {
> +    if (qemu_savevm_send_packaged(ms->file, bioc->data, bioc->usage)) {
>          goto fail_closefb;
>      }
>      qemu_fclose(fb);
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 0ad1b93..f2e1880 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -50,6 +50,7 @@
>  #include "qemu/iov.h"
>  #include "block/snapshot.h"
>  #include "block/qapi.h"
> +#include "io/channel-buffer.h"
>  
>  
>  #ifndef ETH_P_RARP
> @@ -760,10 +761,8 @@ void qemu_savevm_send_open_return_path(QEMUFile *f)
>   *    0 on success
>   *    -ve on error
>   */
> -int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb)
> +int qemu_savevm_send_packaged(QEMUFile *f, const char *buf, size_t len)
>  {
> -    size_t cur_iov;
> -    size_t len = qsb_get_length(qsb);
>      uint32_t tmp;
>  
>      if (len > MAX_VM_CMD_PACKAGED_SIZE) {
> @@ -777,18 +776,7 @@ int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb)
>      trace_qemu_savevm_send_packaged();
>      qemu_savevm_command_send(f, MIG_CMD_PACKAGED, 4, (uint8_t *)&tmp);
>  
> -    /* all the data follows (concatinating the iov's) */
> -    for (cur_iov = 0; cur_iov < qsb->n_iov; cur_iov++) {
> -        /* The iov entries are partially filled */
> -        size_t towrite = MIN(qsb->iov[cur_iov].iov_len, len);
> -        len -= towrite;
> -
> -        if (!towrite) {
> -            break;
> -        }
> -
> -        qemu_put_buffer(f, qsb->iov[cur_iov].iov_base, towrite);
> -    }
> +    qemu_put_buffer(f, (const uint8_t *)buf, len);
>  
>      return 0;
>  }
> @@ -1548,9 +1536,8 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis)
>  static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis)
>  {
>      int ret;
> -    uint8_t *buffer;
>      uint32_t length;
> -    QEMUSizedBuffer *qsb;
> +    QIOChannelBuffer *bioc;
>  
>      length = qemu_get_be32(mis->from_src_file);
>      trace_loadvm_handle_cmd_packaged(length);
> @@ -1559,28 +1546,26 @@ static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis)
>          error_report("Unreasonably large packaged state: %u", length);
>          return -1;
>      }
> -    buffer = g_malloc0(length);
> -    ret = qemu_get_buffer(mis->from_src_file, buffer, (int)length);
> +
> +    bioc = qio_channel_buffer_new(length);
> +    ret = qemu_get_buffer(mis->from_src_file,
> +                          (uint8_t *)bioc->data,
> +                          (int)length);

Actually, qemu_get_buffer takes a size_t now; so you can fix that at the same time.

>      if (ret != length) {
> -        g_free(buffer);
> +        object_unref(OBJECT(bioc));
>          error_report("CMD_PACKAGED: Buffer receive fail ret=%d length=%d\n",
>                  ret, length);
>          return (ret < 0) ? ret : -EAGAIN;
>      }
> +    bioc->usage += length;

I'm a bit surprised you've not wrapped feeding the data
into the qio_channel_buffer up a bit rather than having the callers
prod at it's buffer/usage elements directly.

Dave

>      trace_loadvm_handle_cmd_packaged_received(ret);
>  
> -    /* Setup a dummy QEMUFile that actually reads from the buffer */
> -    qsb = qsb_create(buffer, length);
> -    g_free(buffer); /* Because qsb_create copies */
> -    if (!qsb) {
> -        error_report("Unable to create qsb");
> -    }
> -    QEMUFile *packf = qemu_bufopen("r", qsb);
> +    QEMUFile *packf = qemu_fopen_channel_input(QIO_CHANNEL(bioc));
>  
>      ret = qemu_loadvm_state_main(packf, mis);
>      trace_loadvm_handle_cmd_packaged_main(ret);
>      qemu_fclose(packf);
> -    qsb_free(qsb);
> +    object_unref(OBJECT(bioc));
>  
>      return ret;
>  }
> -- 
> 2.5.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK