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| author | Stefano Garzarella <sgarzare@redhat.com> | 2024-06-18 12:05:19 +0200 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2024-07-03 18:14:06 -0400 |
| commit | 4e647fa08586a5ada74cf6d3ae1cdf3a027202cb (patch) | |
| tree | 396296ac8c5ddfb099d088300a9a99d59a3f5b7c /qemu-options.hx | |
| parent | 5ab04420c3de11ae4a573b08b53584a2a0c5dd00 (diff) | |
| download | focaccia-qemu-4e647fa08586a5ada74cf6d3ae1cdf3a027202cb.tar.gz focaccia-qemu-4e647fa08586a5ada74cf6d3ae1cdf3a027202cb.zip | |
hostmem: add a new memory backend based on POSIX shm_open()
shm_open() creates and opens a new POSIX shared memory object. A POSIX shared memory object allows creating memory backend with an associated file descriptor that can be shared with external processes (e.g. vhost-user). The new `memory-backend-shm` can be used as an alternative when `memory-backend-memfd` is not available (Linux only), since shm_open() should be provided by any POSIX-compliant operating system. This backend mimics memfd, allocating memory that is practically anonymous. In theory shm_open() requires a name, but this is allocated for a short time interval and shm_unlink() is called right after shm_open(). After that, only fd is shared with external processes (e.g., vhost-user) as if it were associated with anonymous memory. In the future we may also allow the user to specify the name to be passed to shm_open(), but for now we keep the backend simple, mimicking anonymous memory such as memfd. Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Stefan Hajnoczi <stefanha@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> (QAPI schema) Signed-off-by: Stefano Garzarella <sgarzare@redhat.com> Message-Id: <20240618100519.145853-1-sgarzare@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'qemu-options.hx')
| -rw-r--r-- | qemu-options.hx | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/qemu-options.hx b/qemu-options.hx index 8ca7f34ef0..ad6521ef5e 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -5240,6 +5240,22 @@ SRST The ``share`` boolean option is on by default with memfd. + ``-object memory-backend-shm,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave`` + Creates a POSIX shared memory backend object, which allows + QEMU to share the memory with an external process (e.g. when + using vhost-user). + + ``memory-backend-shm`` is a more portable and less featureful version + of ``memory-backend-memfd``. It can then be used in any POSIX system, + especially when memfd is not supported. + + Please refer to ``memory-backend-file`` for a description of the + options. + + The ``share`` boolean option is on by default with shm. Setting it to + off will cause a failure during allocation because it is not supported + by this backend. + ``-object iommufd,id=id[,fd=fd]`` Creates an iommufd backend which allows control of DMA mapping through the ``/dev/iommu`` device. |