[Qemu-devel] Regression caused by d2f39ad "exec.c: Ensure right alignment also for file backed ram"

[Haozhong Zhang]

Hi,

Commit d2f39ad "exec.c: Ensure right alignment also for file backed
ram" added an additional alignment requirement besides to the previous
page size for the size of the backend file. On x86, the alignment
requirement for the size of the backend file is changed from 4KB in
QEMU 2.6 to 2MB in QEMU 2.7.

This change immediately breaks the usage of "-object 
memory-backend-file,...,size=$SIZE"
on x86, where $SIZE is multiple of 4KB but not 2MB. It works on QEMU 2.6.
Could this be considered as a regression?

The commit message shows it's for s390. I'm wondering whether the same
regression happens on s390 and ARM. If not, could I fix the regression
on x86 by keeping using the original alignment only on x86, e.g.

modified   exec.c
@@ -1254,7 +1254,11 @@ static void *file_ram_alloc(RAMBlock *block,
    }

    block->page_size = qemu_fd_getpagesize(fd);
+#if defined(__x86_64__) || defined(__i386__)
+    block->mr->align = block->page_size;
+#else
    block->mr->align = MAX(block->page_size, QEMU_VMALLOC_ALIGN);
+#endif

    if (memory < block->page_size) {
        error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "


Thanks,
Haozhong