Re: [Qemu-devel] [PATCH v2 3/3] hostmem-file: make option 'size' optional

[Eduardo Habkost]

On Fri, Oct 28, 2016 at 10:06:40AM +0800, Haozhong Zhang wrote:
[...]
> > > diff --git a/exec.c b/exec.c
> > > index 264a25f..89065bd 100644
> > > --- a/exec.c
> > > +++ b/exec.c
> > > @@ -1234,7 +1234,7 @@ static int64_t get_file_size(int fd)
> > >  }
> > > 
> > >  static void *file_ram_alloc(RAMBlock *block,
> > > -                            ram_addr_t memory,
> > > +                            ram_addr_t *memory,
> > >                              const char *path,
> > >                              Error **errp)
> > >  {
> > > @@ -1245,6 +1245,7 @@ static void *file_ram_alloc(RAMBlock *block,
> > >      void *area = MAP_FAILED;
> > >      int fd = -1;
> > >      int64_t file_size;
> > > +    ram_addr_t mem_size = *memory;
> > > 
> > >      if (kvm_enabled() && !kvm_has_sync_mmu()) {
> > >          error_setg(errp,
> > > @@ -1309,21 +1310,27 @@ static void *file_ram_alloc(RAMBlock *block,
> > > 
> > >      file_size = get_file_size(fd);
> > > 
> > > -    if (memory < block->page_size) {
> > > +    if (!mem_size && file_size > 0) {
> > > +        mem_size = file_size;
> > 
> > Maybe we should set *memory here and not below?
> > 
> 
> Qemu currently sets the memory region size to the file size, and block
> length to the aligned file size, so the code here can be changed as below:
> 
>            memory_region_set_size(block->mr, mem_size);
>            mem_size = HOST_PAGE_ALIGN(mem_size);
>            *memory = mem_size;
> 
> The second line is necessary because Qemu currently passes the aligned
> file size to file_ram_alloc().

That would duplicate the existing HOST_PAGE_ALIGN logic from
qemu_ram_alloc_from_file(), won't it?

I believe that's yet another reason to check file size before
initializing the memory region, instead of initializing it first,
and fixing up its size later.

-- 
Eduardo