From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Fabiano Rosas <farosas@suse.de>
Cc: qemu-devel@nongnu.org, armbru@redhat.com,
Peter Xu <peterx@redhat.com>, Claudio Fontana <cfontana@suse.de>,
Jim Fehlig <jfehlig@suse.com>
Subject: Re: [PATCH 8/9] migration: Add support for fdset with multifd + file
Date: Wed, 8 May 2024 09:53:48 +0100 [thread overview]
Message-ID: <Zjs9nI_Wgi5UIJba@redhat.com> (raw)
In-Reply-To: <20240426142042.14573-9-farosas@suse.de>
On Fri, Apr 26, 2024 at 11:20:41AM -0300, Fabiano Rosas wrote:
> Allow multifd to use an fdset when migrating to a file. This is useful
> for the scenario where the management layer wants to have control over
> the migration file.
>
> By receiving the file descriptors directly, QEMU can delegate some
> high level operating system operations to the management layer (such
> as mandatory access control). The management layer might also want to
> add its own headers before the migration stream.
>
> Enable the "file:/dev/fdset/#" syntax for the multifd migration with
> mapped-ram. The requirements for the fdset mechanism are:
>
> On the migration source side:
>
> - the fdset must contain two fds that are not duplicates between
> themselves;
> - if direct-io is to be used, exactly one of the fds must have the
> O_DIRECT flag set;
> - the file must be opened with WRONLY both times.
>
> On the migration destination side:
>
> - the fdset must contain one fd;
> - the file must be opened with RDONLY.
>
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
> docs/devel/migration/main.rst | 18 ++++++++++++++
> docs/devel/migration/mapped-ram.rst | 6 ++++-
> migration/file.c | 38 ++++++++++++++++++++++++++++-
> 3 files changed, 60 insertions(+), 2 deletions(-)
>
> diff --git a/docs/devel/migration/main.rst b/docs/devel/migration/main.rst
> index 54385a23e5..50f6096470 100644
> --- a/docs/devel/migration/main.rst
> +++ b/docs/devel/migration/main.rst
> @@ -47,6 +47,24 @@ over any transport.
> QEMU interference. Note that QEMU does not flush cached file
> data/metadata at the end of migration.
>
> + The file migration also supports using a file that has already been
> + opened. A set of file descriptors is passed to QEMU via an "fdset"
> + (see add-fd QMP command documentation). This method allows a
> + management application to have control over the migration file
> + opening operation. There are, however, strict requirements to this
> + interface:
> +
> + On the migration source side:
> + - if the multifd capability is to be used, the fdset must contain
> + two file descriptors that are not duplicates between themselves;
> + - if the direct-io capability is to be used, exactly one of the
> + file descriptors must have the O_DIRECT flag set;
> + - the file must be opened with WRONLY.
> +
> + On the migration destination side:
> + - the fdset must contain one file descriptor;
> + - the file must be opened with RDONLY.
> +
> In addition, support is included for migration using RDMA, which
> transports the page data using ``RDMA``, where the hardware takes care of
> transporting the pages, and the load on the CPU is much lower. While the
> diff --git a/docs/devel/migration/mapped-ram.rst b/docs/devel/migration/mapped-ram.rst
> index fa4cefd9fc..e6505511f0 100644
> --- a/docs/devel/migration/mapped-ram.rst
> +++ b/docs/devel/migration/mapped-ram.rst
> @@ -16,7 +16,7 @@ location in the file, rather than constantly being added to a
> sequential stream. Having the pages at fixed offsets also allows the
> usage of O_DIRECT for save/restore of the migration stream as the
> pages are ensured to be written respecting O_DIRECT alignment
> -restrictions (direct-io support not yet implemented).
> +restrictions.
>
> Usage
> -----
> @@ -35,6 +35,10 @@ Use a ``file:`` URL for migration:
> Mapped-ram migration is best done non-live, i.e. by stopping the VM on
> the source side before migrating.
>
> +For best performance enable the ``direct-io`` capability as well:
> +
> + ``migrate_set_capability direct-io on``
> +
> Use-cases
> ---------
>
> diff --git a/migration/file.c b/migration/file.c
> index b9265b14dd..3bc8bc7463 100644
> --- a/migration/file.c
> +++ b/migration/file.c
> @@ -17,6 +17,7 @@
> #include "io/channel-file.h"
> #include "io/channel-socket.h"
> #include "io/channel-util.h"
> +#include "monitor/monitor.h"
> #include "options.h"
> #include "trace.h"
>
> @@ -54,10 +55,18 @@ static void file_remove_fdset(void)
> }
> }
>
> +/*
> + * With multifd, due to the behavior of the dup() system call, we need
> + * the fdset to have two non-duplicate fds so we can enable direct IO
> + * in the secondary channels without affecting the main channel.
> + */
> static bool file_parse_fdset(const char *filename, int64_t *fdset_id,
> Error **errp)
> {
> + FdsetInfoList *fds_info;
> + FdsetFdInfoList *fd_info;
> const char *fdset_id_str;
> + int nfds = 0;
>
> *fdset_id = -1;
>
> @@ -71,6 +80,32 @@ static bool file_parse_fdset(const char *filename, int64_t *fdset_id,
> return false;
> }
>
> + if (!migrate_multifd() || !migrate_direct_io()) {
> + return true;
> + }
> +
> + for (fds_info = qmp_query_fdsets(NULL); fds_info;
> + fds_info = fds_info->next) {
> +
> + if (*fdset_id != fds_info->value->fdset_id) {
> + continue;
> + }
> +
> + for (fd_info = fds_info->value->fds; fd_info; fd_info = fd_info->next) {
> + if (nfds++ > 2) {
> + break;
> + }
> + }
> + }
> +
> + if (nfds != 2) {
> + error_setg(errp, "Outgoing migration needs two fds in the fdset, "
> + "got %d", nfds);
> + qmp_remove_fd(*fdset_id, false, -1, NULL);
> + *fdset_id = -1;
> + return false;
> + }
> +
> return true;
> }
Related to my thoughts in an earlier patch, where I say that use of fdsets
ought to be transparent to QEMU code, I'm not a fan of having this logic
in migration code.
IIUC, the migration code will call qio_channel_file_new_path twice,
once with O_DIRECT and once without. This should trigger two calls
into monitor_fdset_dup_fd_add with different flags. If we're matching
flags in that monitor_fdset_dup_fd_add(), then if only 1 FD was
provided, are we not able to report an error there ?
>
> @@ -209,10 +244,11 @@ void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp)
> g_autofree char *filename = g_strdup(file_args->filename);
> QIOChannelFile *fioc = NULL;
> uint64_t offset = file_args->offset;
> + int flags = O_RDONLY;
>
> trace_migration_file_incoming(filename);
>
> - fioc = qio_channel_file_new_path(filename, O_RDONLY, 0, errp);
> + fioc = qio_channel_file_new_path(filename, flags, 0, errp);
> if (!fioc) {
> return;
> }
> --
> 2.35.3
>
With regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
next prev parent reply other threads:[~2024-05-08 8:54 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 14:20 [PATCH 0/9] migration/mapped-ram: Add direct-io support Fabiano Rosas
2024-04-26 14:20 ` [PATCH 1/9] monitor: Honor QMP request for fd removal immediately Fabiano Rosas
2024-05-03 16:02 ` Peter Xu
2024-05-16 21:46 ` Fabiano Rosas
2024-05-08 7:17 ` Daniel P. Berrangé
2024-05-16 22:00 ` Fabiano Rosas
2024-05-17 7:33 ` Daniel P. Berrangé
2024-04-26 14:20 ` [PATCH 2/9] migration: Fix file migration with fdset Fabiano Rosas
2024-05-03 16:23 ` Peter Xu
2024-05-03 19:56 ` Fabiano Rosas
2024-05-03 21:04 ` Peter Xu
2024-05-03 21:31 ` Fabiano Rosas
2024-05-03 21:56 ` Peter Xu
2024-05-08 8:02 ` Daniel P. Berrangé
2024-05-08 12:49 ` Peter Xu
2024-05-08 8:00 ` Daniel P. Berrangé
2024-05-08 20:45 ` Fabiano Rosas
2024-04-26 14:20 ` [PATCH 3/9] tests/qtest/migration: Fix file migration offset check Fabiano Rosas
2024-05-03 16:47 ` Peter Xu
2024-05-03 20:36 ` Fabiano Rosas
2024-05-03 21:08 ` Peter Xu
2024-05-08 8:10 ` Daniel P. Berrangé
2024-04-26 14:20 ` [PATCH 4/9] migration: Add direct-io parameter Fabiano Rosas
2024-04-26 14:33 ` Markus Armbruster
2024-05-03 18:05 ` Peter Xu
2024-05-03 20:49 ` Fabiano Rosas
2024-05-03 21:16 ` Peter Xu
2024-05-14 14:10 ` Markus Armbruster
2024-05-14 17:57 ` Fabiano Rosas
2024-05-15 7:17 ` Markus Armbruster
2024-05-15 12:51 ` Fabiano Rosas
2024-05-08 8:25 ` Daniel P. Berrangé
2024-04-26 14:20 ` [PATCH 5/9] migration/multifd: Add direct-io support Fabiano Rosas
2024-05-03 18:29 ` Peter Xu
2024-05-03 20:54 ` Fabiano Rosas
2024-05-03 21:18 ` Peter Xu
2024-05-08 8:27 ` Daniel P. Berrangé
2024-04-26 14:20 ` [PATCH 6/9] tests/qtest/migration: Add tests for file migration with direct-io Fabiano Rosas
2024-05-03 18:38 ` Peter Xu
2024-05-03 21:05 ` Fabiano Rosas
2024-05-03 21:25 ` Peter Xu
2024-05-08 8:34 ` Daniel P. Berrangé
2024-04-26 14:20 ` [PATCH 7/9] monitor: fdset: Match against O_DIRECT Fabiano Rosas
2024-05-03 18:53 ` Peter Xu
2024-05-03 21:19 ` Fabiano Rosas
2024-05-03 22:16 ` Peter Xu
2024-04-26 14:20 ` [PATCH 8/9] migration: Add support for fdset with multifd + file Fabiano Rosas
2024-05-08 8:53 ` Daniel P. Berrangé [this message]
2024-05-08 18:23 ` Peter Xu
2024-05-08 20:39 ` Fabiano Rosas
2024-05-09 8:08 ` Daniel P. Berrangé
2024-05-17 22:43 ` Fabiano Rosas
2024-05-18 8:36 ` Daniel P. Berrangé
2024-04-26 14:20 ` [PATCH 9/9] tests/qtest/migration: Add a test for mapped-ram with passing of fds Fabiano Rosas
2024-05-08 8:56 ` Daniel P. Berrangé
2024-05-02 20:01 ` [PATCH 0/9] migration/mapped-ram: Add direct-io support Peter Xu
2024-05-02 20:34 ` Fabiano Rosas
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Zjs9nI_Wgi5UIJba@redhat.com \
--to=berrange@redhat.com \
--cc=armbru@redhat.com \
--cc=cfontana@suse.de \
--cc=farosas@suse.de \
--cc=jfehlig@suse.com \
--cc=peterx@redhat.com \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).