From 090cdb81ce6913f1c5989853d0af0dbb2f1d3f9f Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 20 Nov 2024 11:01:32 -0500 Subject: [PATCH] migration: Allow pipes to keep working for fd migrations MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Peter Xu RH-MergeRequest: 301: migration: Allow pipes to keep working for fd migrations RH-Jira: RHEL-66089 RH-Acked-by: Juraj Marcin RH-Acked-by: Miroslav Rezanina RH-Commit: [1/1] 8b62be63720f81e9d1633844917ab6992d99566f (peterx/qemu-kvm) Libvirt may still use pipes for old file migrations in fd: URI form, especially when loading old images dumped from Libvirt's compression algorithms. In that case, Libvirt needs to compress / uncompress the images on its own over the migration binary stream, and pipes are passed over to QEMU for outgoing / incoming migrations in "fd:" URIs. For future such use case, it should be suggested to use mapped-ram when saving such VM image. However there can still be old images that was compressed in such way, so libvirt needs to be able to load those images, uncompress them and use the same pipe mechanism to pass that over to QEMU. It means, even if new file migrations can be gradually moved over to mapped-ram (after Libvirt start supporting it), Libvirt still needs the uncompressor for the old images to be able to load like before. Meanwhile since Libvirt currently exposes the compression capability to guest images, it may needs its own lifecycle management to move that over to mapped-ram, maybe can be done after mapped-ram saved the image, however Dan and PeterK raised concern on temporary double disk space consumption. I suppose for now the easiest is to enable pipes for both sides of "fd:" migrations, until all things figured out from Libvirt side on how to move on. And for "channels" QMP interface support on "migrate" / "migrate-incoming" commands, we'll also need to move away from pipe. But let's leave that for later too. So far, still allow pipes to happen like before on both save/load sides, just like we would allow sockets to pass. Cc: qemu-stable Cc: Fabiano Rosas Cc: Peter Krempa Cc: Daniel P. Berrangé Fixes: c55deb860c ("migration: Deprecate fd: for file migration") Reviewed-by: Fabiano Rosas Link: https://lore.kernel.org/r/20241120160132.3659735-1-peterx@redhat.com Signed-off-by: Peter Xu (cherry picked from commit 87ae45e602e2943d58509e470e3a1d4ba084ab2f) Signed-off-by: Peter Xu --- migration/fd.c | 27 +++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) diff --git a/migration/fd.c b/migration/fd.c index aab5189eac..9bf9be6acb 100644 --- a/migration/fd.c +++ b/migration/fd.c @@ -25,6 +25,29 @@ #include "io/channel-util.h" #include "trace.h" +static bool fd_is_pipe(int fd) +{ + struct stat statbuf; + + if (fstat(fd, &statbuf) == -1) { + return false; + } + + return S_ISFIFO(statbuf.st_mode); +} + +static bool migration_fd_valid(int fd) +{ + if (fd_is_socket(fd)) { + return true; + } + + if (fd_is_pipe(fd)) { + return true; + } + + return false; +} void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp) { @@ -34,7 +57,7 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error ** return; } - if (!fd_is_socket(fd)) { + if (!migration_fd_valid(fd)) { warn_report("fd: migration to a file is deprecated." " Use file: instead."); } @@ -68,7 +91,7 @@ void fd_start_incoming_migration(const char *fdname, Error **errp) return; } - if (!fd_is_socket(fd)) { + if (!migration_fd_valid(fd)) { warn_report("fd: migration to a file is deprecated." " Use file: instead."); } -- 2.39.3