Re: [PATCH v5 17/23] migration/multifd: Add outgoing QIOChannelFile support

[Fabiano Rosas]

Peter Xu <peterx@redhat.com> writes:

> On Thu, Feb 29, 2024 at 10:44:21AM +0800, Peter Xu wrote:
>> On Wed, Feb 28, 2024 at 12:21:21PM -0300, Fabiano Rosas wrote:
>> > Allow multifd to open file-backed channels. This will be used when
>> > enabling the mapped-ram migration stream format which expects a
>> > seekable transport.
>> > 
>> > The QIOChannel read and write methods will use the preadv/pwritev
>> > versions which don't update the file offset at each call so we can
>> > reuse the fd without re-opening for every channel.
>> > 
>> > Contrary to the socket migration, the file migration doesn't need an
>> > asynchronous channel creation process, so expose
>> > multifd_channel_connect() and call it directly.
>> > 
>> > Note that this is just setup code and multifd cannot yet make use of
>> > the file channels.
>> > 
>> > Signed-off-by: Fabiano Rosas <farosas@suse.de>
>> > ---
>> > - moved flags change to another patch
>> > - removed channels_created assert
>> > ---
>> >  migration/file.c    | 41 +++++++++++++++++++++++++++++++++++++++--
>> >  migration/file.h    |  4 ++++
>> >  migration/multifd.c | 18 +++++++++++++++---
>> >  migration/multifd.h |  1 +
>> >  4 files changed, 59 insertions(+), 5 deletions(-)
>> > 
>> > diff --git a/migration/file.c b/migration/file.c
>> > index 22d052a71f..83328a7a1b 100644
>> > --- a/migration/file.c
>> > +++ b/migration/file.c
>> > @@ -12,12 +12,17 @@
>> >  #include "channel.h"
>> >  #include "file.h"
>> >  #include "migration.h"
>> > +#include "multifd.h"
>> >  #include "io/channel-file.h"
>> >  #include "io/channel-util.h"
>> >  #include "trace.h"
>> >  
>> >  #define OFFSET_OPTION ",offset="
>> >  
>> > +static struct FileOutgoingArgs {
>> > +    char *fname;
>> > +} outgoing_args;
>> > +
>> >  /* Remove the offset option from @filespec and return it in @offsetp. */
>> >  
>> >  int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
>> > @@ -37,6 +42,36 @@ int file_parse_offset(char *filespec, uint64_t 
>> > *offsetp, Error **errp)
>> >      return 0;
>> >  }
>> >  
>> > +void file_cleanup_outgoing_migration(void)
>> > +{
>> > +    g_free(outgoing_args.fname);
>> > +    outgoing_args.fname = NULL;
>> > +}
>> > +
>> > +bool file_send_channel_create(gpointer opaque, Error **errp)
>> > +{
>> > +    QIOChannelFile *ioc;
>> > +    int flags = O_WRONLY;
>> > +    bool ret = true;
>> > +
>> > +    ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
>> > +    if (!ioc) {
>> > +        ret = false;
>> > +        goto out;
>> > +    }
>> > +
>> > +    multifd_channel_connect(opaque, QIO_CHANNEL(ioc));
>> > +
>> > +out:
>> > +    /*
>> > +     * File channel creation is synchronous. However posting this
>> > +     * semaphore here is simpler than adding a special case.
>> > +     */
>> > +    multifd_send_channel_created();
>> > +
>> > +    return ret;
>> > +}
>> > +
>> >  void file_start_outgoing_migration(MigrationState *s,
>> >                                     FileMigrationArgs *file_args, Error 
>> > **errp)
>> >  {
>> > @@ -47,12 +82,14 @@ void file_start_outgoing_migration(MigrationState *s,
>> >  
>> >      trace_migration_file_outgoing(filename);
>> >  
>> > -    fioc = qio_channel_file_new_path(filename, O_CREAT | O_WRONLY | 
>> > O_TRUNC,
>> > -                                     0600, errp);
>> > +    fioc = qio_channel_file_new_path(filename, O_CREAT | O_TRUNC | 
>> > O_WRONLY,
>> > +                                     0660, errp);
>> 
>> It seems this is still leftover?
>> 
>> >      if (!fioc) {
>> >          return;
>> >      }
>> >  
>> > +    outgoing_args.fname = g_strdup(filename);
>> > +
>> >      ioc = QIO_CHANNEL(fioc);
>> >      if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
>> >          return;
>> > diff --git a/migration/file.h b/migration/file.h
>> > index 37d6a08bfc..4577f9efdd 100644
>> > --- a/migration/file.h
>> > +++ b/migration/file.h
>> > @@ -9,10 +9,14 @@
>> >  #define QEMU_MIGRATION_FILE_H
>> >  
>> >  #include "qapi/qapi-types-migration.h"
>> > +#include "io/task.h"
>> > +#include "channel.h"
>> >  
>> >  void file_start_incoming_migration(FileMigrationArgs *file_args, Error 
>> > **errp);
>> >  
>> >  void file_start_outgoing_migration(MigrationState *s,
>> >                                     FileMigrationArgs *file_args, Error 
>> > **errp);
>> >  int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp);
>> > +void file_cleanup_outgoing_migration(void);
>> > +bool file_send_channel_create(gpointer opaque, Error **errp);
>> >  #endif
>> > diff --git a/migration/multifd.c b/migration/multifd.c
>> > index 3574fd3953..f155223303 100644
>> > --- a/migration/multifd.c
>> > +++ b/migration/multifd.c
>> > @@ -17,6 +17,7 @@
>> >  #include "exec/ramblock.h"
>> >  #include "qemu/error-report.h"
>> >  #include "qapi/error.h"
>> > +#include "file.h"
>> >  #include "ram.h"
>> >  #include "migration.h"
>> >  #include "migration-stats.h"
>> > @@ -28,6 +29,7 @@
>> >  #include "threadinfo.h"
>> >  #include "options.h"
>> >  #include "qemu/yank.h"
>> > +#include "io/channel-file.h"
>> >  #include "io/channel-socket.h"
>> >  #include "yank_functions.h"
>> >  
>> > @@ -694,6 +696,7 @@ static bool 
>> > multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
>> >  {
>> >      if (p->c) {
>> >          migration_ioc_unregister_yank(p->c);
>> > +        qio_channel_close(p->c, NULL);
>> 
>> s/NULL/&error_abort/?
>
> Or we can drop this line?  IIUC iochannel finalize() will always close it,
> or it could be a separate bug.
>

We need it so the fsync happens. The finalize() will be a noop because
the qio_channel_file_close() will clear the fd. Not the cleanest, but it
works.

>> 
>> >          object_unref(OBJECT(p->c));
>> >          p->c = NULL;
>> >      }
>> > @@ -715,6 +718,7 @@ static bool 
>> > multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
>> >  
>> >  static void multifd_send_cleanup_state(void)
>> >  {
>> > +    file_cleanup_outgoing_migration();
>> >      socket_cleanup_outgoing_migration();
>> >      qemu_sem_destroy(&multifd_send_state->channels_created);
>> >      qemu_sem_destroy(&multifd_send_state->channels_ready);
>> > @@ -977,7 +981,7 @@ static bool 
>> > multifd_tls_channel_connect(MultiFDSendParams *p,
>> >      return true;
>> >  }
>> >  
>> > -static void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc)
>> > +void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc)
>> >  {
>> >      qio_channel_set_delay(ioc, false);
>> >  
>> > @@ -1045,9 +1049,14 @@ out:
>> >      error_free(local_err);
>> >  }
>> >  
>> > -static void multifd_new_send_channel_create(gpointer opaque)
>> > +static bool multifd_new_send_channel_create(gpointer opaque, Error **errp)
>> >  {
>> > +    if (!multifd_use_packets()) {
>> > +        return file_send_channel_create(opaque, errp);
>> > +    }
>> > +
>> >      socket_send_channel_create(multifd_new_send_channel_async, opaque);
>> > +    return true;
>> >  }
>> >  
>> >  bool multifd_send_setup(void)
>> > @@ -1096,7 +1105,10 @@ bool multifd_send_setup(void)
>> >          p->page_size = qemu_target_page_size();
>> >          p->page_count = page_count;
>> >          p->write_flags = 0;
>> > -        multifd_new_send_channel_create(p);
>> > +
>> > +        if (!multifd_new_send_channel_create(p, &local_err)) {
>> > +            return -1;
>> 
>> "-1" is unfortunately a "true"!..
>> 
>> > +        }
>> >      }
>> >  
>> >      /*
>> > diff --git a/migration/multifd.h b/migration/multifd.h
>> > index 1d8bbaf96b..db8887f088 100644
>> > --- a/migration/multifd.h
>> > +++ b/migration/multifd.h
>> > @@ -227,5 +227,6 @@ static inline void 
>> > multifd_send_prepare_header(MultiFDSendParams *p)
>> >      p->iovs_num++;
>> >  }
>> >  
>> > +void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc);
>> >  
>> >  #endif
>> > -- 
>> > 2.35.3
>> > 
>> 
>> -- 
>> Peter Xu