Stefano Garzarella <sgarz...@redhat.com> writes:
> 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 <da...@redhat.com>
> Acked-by: Stefan Hajnoczi <stefa...@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
[...]
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 9b8f6a7ab5..94e4458288 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -601,8 +601,8 @@
> #
> # @share: if false, the memory is private to QEMU; if true, it is
> # shared (default false for backends memory-backend-file and
> -# memory-backend-ram, true for backends memory-backend-epc and
> -# memory-backend-memfd)
> +# memory-backend-ram, true for backends memory-backend-epc,
> +# memory-backend-memfd, and memory-backend-shm)
> #
> # @reserve: if true, reserve swap space (or huge pages) if applicable
> # (default: true) (since 6.1)
> @@ -721,6 +721,22 @@
> '*hugetlbsize': 'size',
> '*seal': 'bool' } }
>
> +##
> +# @MemoryBackendShmProperties:
> +#
> +# Properties for memory-backend-shm objects.
> +#
> +# Setting @share boolean option (defined in the base type) to false
> +# will cause a failure during allocation because it is not
> +# supported by this backend.
This is QMP reference documentation. "Failure during allocation" feels
like unnecessary detail there. Maybe "This memory backend support only
shared memory, which is the default."
> +#
> +# Since: 9.1
> +##
> +{ 'struct': 'MemoryBackendShmProperties',
> + 'base': 'MemoryBackendProperties',
> + 'data': { },
> + 'if': 'CONFIG_POSIX' }
> +
> ##
> # @MemoryBackendEpcProperties:
> #
> @@ -1049,6 +1065,8 @@
> { 'name': 'memory-backend-memfd',
> 'if': 'CONFIG_LINUX' },
> 'memory-backend-ram',
> + { 'name': 'memory-backend-shm',
> + 'if': 'CONFIG_POSIX' },
> 'pef-guest',
> { 'name': 'pr-manager-helper',
> 'if': 'CONFIG_LINUX' },
> @@ -1121,6 +1139,8 @@
> 'memory-backend-memfd': { 'type': 'MemoryBackendMemfdProperties',
> 'if': 'CONFIG_LINUX' },
> 'memory-backend-ram': 'MemoryBackendProperties',
> + 'memory-backend-shm': { 'type': 'MemoryBackendShmProperties',
> + 'if': 'CONFIG_POSIX' },
> 'pr-manager-helper': { 'type': 'PrManagerHelperProperties',
> 'if': 'CONFIG_LINUX' },
> 'qtest': 'QtestProperties',
[...]
Other than that, QAPI schema
Acked-by: Markus Armbruster <arm...@redhat.com>
