Create MAP_SHARED RAMBlocks by mmap'ing a file descriptor rather than using
MAP_ANON, so the memory can be accessed in another process by passing and
mmap'ing the fd. This will allow CPR to support memory-backend-ram and
memory-backend-shm objects, provided the user creates them with share=on.
Use memfd_create if available because it has no constraints. If not, use
POSIX shm_open. However, allocation on the opened fd may fail if the shm
mount size is too small, even if the system has free memory, so for backwards
compatibility fall back to qemu_anon_ram_alloc/MAP_ANON on failure.
For backwards compatibility on Windows, always use MAP_ANON. share=on has
no purpose there, but the syntax is accepted, and must continue to work.
Lastly, quietly fall back to MAP_ANON if the system does not support
qemu_ram_alloc_from_fd.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-5-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
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