hostmem-file: add "align" option
When mmap(2) the backend files, QEMU uses the host page size
(getpagesize(2)) by default as the alignment of mapping address.
However, some backends may require alignments different than the page
size. For example, mmap a device DAX (e.g., /dev/dax0.0) on Linux
kernel 4.13 to an address, which is 4K-aligned but not 2M-aligned,
fails with a kernel message like
[617494.969768] dax dax0.0: qemu-system-x86: dax_mmap: fail, unaligned vma (0x7fa37c579000 - 0x7fa43c579000, 0x1fffff)
Because there is no common approach to get such alignment requirement,
we add the 'align' option to 'memory-backend-file', so that users or
management utils, which have enough knowledge about the backend, can
specify a proper alignment via this option.
Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Message-Id: <20171211072806.2812-2-haozhong.zhang@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
[ehabkost: fixed typo, fixed error_setg() format string]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
diff --git a/exec.c b/exec.c
index d28fc0c..629a508 100644
--- a/exec.c
+++ b/exec.c
@@ -1612,7 +1612,13 @@
void *area;
block->page_size = qemu_fd_getpagesize(fd);
- block->mr->align = block->page_size;
+ if (block->mr->align % block->page_size) {
+ error_setg(errp, "alignment 0x%" PRIx64
+ " must be multiples of page size 0x%zx",
+ block->mr->align, block->page_size);
+ return NULL;
+ }
+ block->mr->align = MAX(block->page_size, block->mr->align);
#if defined(__s390x__)
if (kvm_enabled()) {
block->mr->align = MAX(block->mr->align, QEMU_VMALLOC_ALIGN);
