On 06.02.20 13:08, Richard Henderson wrote: > On 2/3/20 6:31 PM, David Hildenbrand wrote: >> +void *qemu_ram_mmap_resize(void *ptr, int fd, size_t old_size, size_t >> new_size, >> + bool shared, bool is_pmem) >> { >> const size_t pagesize = mmap_pagesize(fd); >> >> /* we can only map whole pages */ >> - size = QEMU_ALIGN_UP(size, pagesize); >> + old_size = QEMU_ALIGN_UP(old_size, pagesize); >> + new_size = QEMU_ALIGN_UP(new_size, pagesize); >> + >> + /* we support actually resizable memory regions only on Linux */ >> + if (old_size < new_size) { >> + /* populate the missing piece into the reserved area */ >> + ptr = mmap_populate(ptr + old_size, new_size - old_size, fd, >> old_size, >> + shared, is_pmem); >> + } else if (old_size > new_size) { >> + /* discard this piece, keeping the area reserved (should never >> fail) */ >> + ptr = mmap_reserve(ptr + new_size, old_size - new_size, fd); >> + } >> + return ptr; >> +} > > What does the return value indicate? > Is it just for != MAP_FAILED?
It indicates if resizing succeeded. In a previous version I returned an int via ptr == MAP_FAILED ? -errno : 0; Populating will usually only fail because we're out of memory. Populating and reserving *might* fail if we are out of VMAs in the kernel. VMA merging will make sure that the number of VMAs will not explode (usually 2-3 VMAs for one resizable region: populated VMA + Reserved VMA + Guard page VMA). But once we would be close to the VMA limit, it could happen - but it's highly unlikely. > Assuming an assert isn't viable, are we better off with a boolean return? > With > an Error **ptr? either that or an int. What do you prefer? Thanks! -- Thanks, David / dhildenb