On Wed, Oct 25, 2023 at 12:00:12PM -0300, Fabiano Rosas wrote:
> Daniel P. Berrangé <berra...@redhat.com> writes:
>
> > On Wed, Oct 25, 2023 at 11:12:38AM -0300, Fabiano Rosas wrote:
> >> Daniel P. Berrangé <berra...@redhat.com> writes:
> >>
> >> > On Mon, Oct 23, 2023 at 05:35:58PM -0300, Fabiano Rosas wrote:
> >> >> Allow multifd to open file-backed channels. This will be used when
> >> >> enabling the fixed-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.
> >> >>
> >> >> Note that this is just setup code and multifd cannot yet make use of
> >> >> the file channels.
> >> >>
> >> >> Signed-off-by: Fabiano Rosas <faro...@suse.de>
> >> >> ---
> >> >> migration/file.c | 64 +++++++++++++++++++++++++++++++++++++++++--
> >> >> migration/file.h | 10 +++++--
> >> >> migration/migration.c | 2 +-
> >> >> migration/multifd.c | 14 ++++++++--
> >> >> migration/options.c | 7 +++++
> >> >> migration/options.h | 1 +
> >> >> 6 files changed, 90 insertions(+), 8 deletions(-)
> >> >>
> >> >> diff --git a/migration/file.c b/migration/file.c
> >> >> index cf5b1bf365..93b9b7bf5d 100644
> >> >> --- a/migration/file.c
> >> >> +++ b/migration/file.c
> >> >> @@ -17,6 +17,12 @@
> >> >
> >> >> +void file_send_channel_create(QIOTaskFunc f, void *data)
> >> >> +{
> >> >> + QIOChannelFile *ioc;
> >> >> + QIOTask *task;
> >> >> + Error *errp = NULL;
> >> >> +
> >> >> + ioc = qio_channel_file_new_path(outgoing_args.fname,
> >> >> + outgoing_args.flags,
> >> >> + outgoing_args.mode, &errp);
> >> >> + if (!ioc) {
> >> >> + file_migration_cancel(errp);
> >> >> + return;
> >> >> + }
> >> >> +
> >> >> + task = qio_task_new(OBJECT(ioc), f, (gpointer)data, NULL);
> >> >> + qio_task_run_in_thread(task, qio_channel_file_connect_worker,
> >> >> + (gpointer)data, NULL, NULL);
> >> >> +}
> >> >> +
> >> >> void file_start_outgoing_migration(MigrationState *s, const char
> >> >> *filespec,
> >> >> Error **errp)
> >> >> {
> >> >> - g_autofree char *filename = g_strdup(filespec);
> >> >> g_autoptr(QIOChannelFile) fioc = NULL;
> >> >> + g_autofree char *filename = g_strdup(filespec);
> >> >> uint64_t offset = 0;
> >> >> QIOChannel *ioc;
> >> >> + int flags = O_CREAT | O_TRUNC | O_WRONLY;
> >> >> + mode_t mode = 0660;
> >> >>
> >> >> trace_migration_file_outgoing(filename);
> >> >>
> >> >> @@ -50,12 +105,15 @@ void file_start_outgoing_migration(MigrationState
> >> >> *s, const char *filespec,
> >> >> return;
> >> >> }
> >> >>
> >> >> - fioc = qio_channel_file_new_path(filename, O_CREAT | O_WRONLY |
> >> >> O_TRUNC,
> >> >> - 0600, errp);
> >>
> >> By the way, we're experimenting with add-fd to flesh out the interface
> >> with libvirt and I see that the flags here can conflict with the flags
> >> set on the fd passed through `virsh --pass-fd ...` due to this at
> >> monitor_fdset_dup_fd_add():
> >>
> >> if ((flags & O_ACCMODE) == (mon_fd_flags & O_ACCMODE)) {
> >> fd = mon_fdset_fd->fd;
> >> break;
> >> }
> >>
> >> We're requiring the O_RDONLY, O_WRONLY, O_RDWR flags defined here to
> >> match the fdset passed into QEMU. Should we just sync the code of the
> >> two projects to use the same flags? That feels a little clumsy to me.
> >
> > Is there a reason for libvirt to have set O_RDONLY for a file used
> > for outgoing migration ? I can't recall off-hand.
> >
>
> The flags need to match exactly, so either libvirt or QEMU could in the
> future decide to use O_RDWR. Then we'd have a compatibility problem when
> passing the fds around.
The "safe" option would be to always open O_RDWR, even if it is
technically redundant for our current needs.
With regards,
Daniel
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