From: Fabiano Rosas <farosas@suse.de>

If we receive a file descriptor that points to a regular file, there's
nothing stopping us from doing multifd migration with mapped-ram to
that file.

Enable the fd: URI to work with multifd + mapped-ram.

Note that the fds passed into multifd are duplicated because we want
to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
original fd doesn't need to be duplicated because monitor_get_fd()
transfers ownership to the caller.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/fd.h        |  2 ++
 migration/fd.c        | 44 +++++++++++++++++++++++++++++++++++++++++++
 migration/file.c      | 18 ++++++++++++------
 migration/migration.c |  4 ++++
 migration/multifd.c   |  2 ++
 5 files changed, 64 insertions(+), 6 deletions(-)

diff --git a/migration/fd.h b/migration/fd.h
index b901bc014e..0c0a18d9e7 100644
--- a/migration/fd.h
+++ b/migration/fd.h
@@ -20,4 +20,6 @@ void fd_start_incoming_migration(const char *fdname, Error **errp);
 
 void fd_start_outgoing_migration(MigrationState *s, const char *fdname,
                                  Error **errp);
+void fd_cleanup_outgoing_migration(void);
+int fd_args_get_fd(void);
 #endif
diff --git a/migration/fd.c b/migration/fd.c
index 0eb677dcae..d4ae72d132 100644
--- a/migration/fd.c
+++ b/migration/fd.c
@@ -15,18 +15,41 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 #include "channel.h"
 #include "fd.h"
 #include "migration.h"
 #include "monitor/monitor.h"
+#include "io/channel-file.h"
 #include "io/channel-util.h"
+#include "options.h"
 #include "trace.h"
 
 
+static struct FdOutgoingArgs {
+    int fd;
+} outgoing_args;
+
+int fd_args_get_fd(void)
+{
+    return outgoing_args.fd;
+}
+
+void fd_cleanup_outgoing_migration(void)
+{
+    if (outgoing_args.fd > 0) {
+        close(outgoing_args.fd);
+        outgoing_args.fd = -1;
+    }
+}
+
 void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
 {
     QIOChannel *ioc;
     int fd = monitor_get_fd(monitor_cur(), fdname, errp);
+
+    outgoing_args.fd = -1;
+
     if (fd == -1) {
         return;
     }
@@ -38,6 +61,8 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
         return;
     }
 
+    outgoing_args.fd = fd;
+
     qio_channel_set_name(ioc, "migration-fd-outgoing");
     migration_channel_connect(s, ioc, NULL, NULL);
     object_unref(OBJECT(ioc));
@@ -73,4 +98,23 @@ void fd_start_incoming_migration(const char *fdname, Error **errp)
                                fd_accept_incoming_migration,
                                NULL, NULL,
                                g_main_context_get_thread_default());
+
+    if (migrate_multifd()) {
+        int channels = migrate_multifd_channels();
+
+        while (channels--) {
+            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));
+
+            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
+                error_setg(errp, "Failed to duplicate fd %d", fd);
+                return;
+            }
+
+            qio_channel_set_name(ioc, "migration-fd-incoming");
+            qio_channel_add_watch_full(ioc, G_IO_IN,
+                                       fd_accept_incoming_migration,
+                                       NULL, NULL,
+                                       g_main_context_get_thread_default());
+        }
+    }
 }
diff --git a/migration/file.c b/migration/file.c
index 499d2782fe..164b079966 100644
--- a/migration/file.c
+++ b/migration/file.c
@@ -11,6 +11,7 @@
 #include "qemu/error-report.h"
 #include "qapi/error.h"
 #include "channel.h"
+#include "fd.h"
 #include "file.h"
 #include "migration.h"
 #include "io/channel-file.h"
@@ -53,15 +54,20 @@ 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;
+    bool ret = false;
+    int fd = fd_args_get_fd();
+
+    if (fd && fd != -1) {
+        ioc = qio_channel_file_new_fd(dup(fd));
+    } else {
+        ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
+        if (!ioc) {
+            goto out;
+        }
     }
 
     multifd_channel_connect(opaque, QIO_CHANNEL(ioc));
+    ret = true;
 
 out:
     /*
diff --git a/migration/migration.c b/migration/migration.c
index b9baab543a..a49fcd53ee 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -140,6 +140,10 @@ static bool transport_supports_multi_channels(MigrationAddress *addr)
     if (addr->transport == MIGRATION_ADDRESS_TYPE_SOCKET) {
         SocketAddress *saddr = &addr->u.socket;
 
+        if (saddr->type == SOCKET_ADDRESS_TYPE_FD) {
+            return migrate_mapped_ram();
+        }
+
         return (saddr->type == SOCKET_ADDRESS_TYPE_INET ||
                 saddr->type == SOCKET_ADDRESS_TYPE_UNIX ||
                 saddr->type == SOCKET_ADDRESS_TYPE_VSOCK);
diff --git a/migration/multifd.c b/migration/multifd.c
index 419feb7df1..b4e5a9dfcc 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 "fd.h"
 #include "file.h"
 #include "migration.h"
 #include "migration-stats.h"
@@ -731,6 +732,7 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
 static void multifd_send_cleanup_state(void)
 {
     file_cleanup_outgoing_migration();
+    fd_cleanup_outgoing_migration();
     socket_cleanup_outgoing_migration();
     qemu_sem_destroy(&multifd_send_state->channels_created);
     qemu_sem_destroy(&multifd_send_state->channels_ready);
-- 
2.44.0

On Mon, Mar 04, 2024 at 09:26:32AM +0800, peterx@redhat.com wrote:
> From: Fabiano Rosas <farosas@suse.de>
> 
> If we receive a file descriptor that points to a regular file, there's
> nothing stopping us from doing multifd migration with mapped-ram to
> that file.
> 
> Enable the fd: URI to work with multifd + mapped-ram.
> 
> Note that the fds passed into multifd are duplicated because we want
> to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
> original fd doesn't need to be duplicated because monitor_get_fd()
> transfers ownership to the caller.
> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/fd.h        |  2 ++
>  migration/fd.c        | 44 +++++++++++++++++++++++++++++++++++++++++++
>  migration/file.c      | 18 ++++++++++++------
>  migration/migration.c |  4 ++++
>  migration/multifd.c   |  2 ++
>  5 files changed, 64 insertions(+), 6 deletions(-)
> 

> @@ -73,4 +98,23 @@ void fd_start_incoming_migration(const char *fdname, Error **errp)
>                                 fd_accept_incoming_migration,
>                                 NULL, NULL,
>                                 g_main_context_get_thread_default());
> +
> +    if (migrate_multifd()) {
> +        int channels = migrate_multifd_channels();
> +
> +        while (channels--) {
> +            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));
> +
> +            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
> +                error_setg(errp, "Failed to duplicate fd %d", fd);
> +                return;
> +            }

I'd suggest that Peter's comment about failure checks be fixed
by introducing a new constructor that handles the dup + error
reporting.

   QIOChannel *qio_channel_file_new_dupfd(int fd, Error **errp;)

so we're not repeating the error reporting multiple places.

> +
> +            qio_channel_set_name(ioc, "migration-fd-incoming");
> +            qio_channel_add_watch_full(ioc, G_IO_IN,
> +                                       fd_accept_incoming_migration,
> +                                       NULL, NULL,
> +                                       g_main_context_get_thread_default());
> +        }
> +    }
>  }

With regards,
Daniel
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On Mon, Mar 11, 2024 at 12:03:41PM +0000, Daniel P. Berrangé wrote:
> On Mon, Mar 04, 2024 at 09:26:32AM +0800, peterx@redhat.com wrote:
> > From: Fabiano Rosas <farosas@suse.de>
> > 
> > If we receive a file descriptor that points to a regular file, there's
> > nothing stopping us from doing multifd migration with mapped-ram to
> > that file.
> > 
> > Enable the fd: URI to work with multifd + mapped-ram.
> > 
> > Note that the fds passed into multifd are duplicated because we want
> > to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
> > original fd doesn't need to be duplicated because monitor_get_fd()
> > transfers ownership to the caller.
> > 
> > Signed-off-by: Fabiano Rosas <farosas@suse.de>
> > Reviewed-by: Peter Xu <peterx@redhat.com>
> > Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  migration/fd.h        |  2 ++
> >  migration/fd.c        | 44 +++++++++++++++++++++++++++++++++++++++++++
> >  migration/file.c      | 18 ++++++++++++------
> >  migration/migration.c |  4 ++++
> >  migration/multifd.c   |  2 ++
> >  5 files changed, 64 insertions(+), 6 deletions(-)
> > 
> 
> > @@ -73,4 +98,23 @@ void fd_start_incoming_migration(const char *fdname, Error **errp)
> >                                 fd_accept_incoming_migration,
> >                                 NULL, NULL,
> >                                 g_main_context_get_thread_default());
> > +
> > +    if (migrate_multifd()) {
> > +        int channels = migrate_multifd_channels();
> > +
> > +        while (channels--) {
> > +            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));
> > +
> > +            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
> > +                error_setg(errp, "Failed to duplicate fd %d", fd);
> > +                return;
> > +            }
> 
> I'd suggest that Peter's comment about failure checks be fixed
> by introducing a new constructor that handles the dup + error
> reporting.
> 
>    QIOChannel *qio_channel_file_new_dupfd(int fd, Error **errp;)
> 
> so we're not repeating the error reporting multiple places.

Indeed that looks cleaner.

At the meantime, I just noticed there seems to have an IOC leak on incoming
side..  file_start_incoming_migration():

    do {
        QIOChannel *ioc = QIO_CHANNEL(fioc);

        qio_channel_set_name(ioc, "migration-file-incoming");
        qio_channel_add_watch_full(ioc, G_IO_IN,
                                   file_accept_incoming_migration,
                                   NULL, NULL,
                                   g_main_context_get_thread_default());

        fioc = qio_channel_file_new_fd(dup(fioc->fd)); <-------------------- here

        if (!fioc || fioc->fd == -1) {
            error_setg(errp, "Error creating migration incoming channel");
            break;
        }
    } while (++i < channels);

Fabiano, would you send patches to address these issues (split if both
issues exist)?

Thanks,

-- 
Peter Xu

On Mon, 4 Mar 2024 at 01:28, <peterx@redhat.com> wrote:
>
> From: Fabiano Rosas <farosas@suse.de>
>
> If we receive a file descriptor that points to a regular file, there's
> nothing stopping us from doing multifd migration with mapped-ram to
> that file.
>
> Enable the fd: URI to work with multifd + mapped-ram.
>
> Note that the fds passed into multifd are duplicated because we want
> to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
> original fd doesn't need to be duplicated because monitor_get_fd()
> transfers ownership to the caller.
>
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
> Signed-off-by: Peter Xu <peterx@redhat.com>

Hi; Coverity points out some issues with this commit (CID 1539961, 1539965):


> @@ -73,4 +98,23 @@ void fd_start_incoming_migration(const char *fdname, Error **errp)
>                                 fd_accept_incoming_migration,
>                                 NULL, NULL,
>                                 g_main_context_get_thread_default());
> +
> +    if (migrate_multifd()) {
> +        int channels = migrate_multifd_channels();
> +
> +        while (channels--) {
> +            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));

dup() can fail and return -1, but we don't check for failure
and pass the return value directly to qio_channel_file_new_fd(),
which will call lseek() on it, which isn't valid.

> +
> +            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
> +                error_setg(errp, "Failed to duplicate fd %d", fd);
> +                return;
> +            }
> +
> +            qio_channel_set_name(ioc, "migration-fd-incoming");
> +            qio_channel_add_watch_full(ioc, G_IO_IN,
> +                                       fd_accept_incoming_migration,
> +                                       NULL, NULL,
> +                                       g_main_context_get_thread_default());
> +        }
> +    }

> @@ -53,15 +54,20 @@ 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;
> +    bool ret = false;
> +    int fd = fd_args_get_fd();
> +
> +    if (fd && fd != -1) {
> +        ioc = qio_channel_file_new_fd(dup(fd));

Similarly here.

> +    } else {
> +        ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
> +        if (!ioc) {
> +            goto out;
> +        }
>      }
>
>      multifd_channel_connect(opaque, QIO_CHANNEL(ioc));
> +    ret = true;
>
>  out:
>      /*

thanks
-- PMM

On Mon, 11 Mar 2024 at 11:50, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Mon, 4 Mar 2024 at 01:28, <peterx@redhat.com> wrote:
> >
> > From: Fabiano Rosas <farosas@suse.de>
> >
> > If we receive a file descriptor that points to a regular file, there's
> > nothing stopping us from doing multifd migration with mapped-ram to
> > that file.
> >
> > Enable the fd: URI to work with multifd + mapped-ram.
> >
> > Note that the fds passed into multifd are duplicated because we want
> > to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
> > original fd doesn't need to be duplicated because monitor_get_fd()
> > transfers ownership to the caller.
> >
> > Signed-off-by: Fabiano Rosas <farosas@suse.de>
> > Reviewed-by: Peter Xu <peterx@redhat.com>
> > Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
> > Signed-off-by: Peter Xu <peterx@redhat.com>
>
> Hi; Coverity points out some issues with this commit (CID 1539961, 1539965):

Oh, and also CID 1539960: there's a third instance of dup() with
no error checking in another commit.

thanks
-- PMM