Re: ramdisk corruption problems - was: RE: pivot_root and initrd

[Alexander Viro]

On Sat, 29 Dec 2001, Andrew Morton wrote:

> Would it be necessary to preallocate the holes at mmap() time?  Mad
> hand-waving: Could we not perform the instantiation at pagefault time,
> and give the caller SIGBUS if we cannot allocate the blocks?  Or if
> there's an IO error, or quota exceeded.

Allocation at mmap() Is Not Going To Happen.  Consider it vetoed.
There are applications that use mmap() on large and very sparse
files.
  
> Question: can someone please define BH_New?  Its lifecycle seems
> very vague.  We never actually seem to *clear* it anywhere for 
> ext2, and it appears that the kernel will keep on treating a
> clearly non-new buffer as "new" all the time.  ext3 explicitly
> clears BH_New in get_block(), if it finds the block was already
> present in the file.  I did this because we need the newness
> info for internal purposes.

It should be reset when we submit IO.  Breakage related to failing
allocation is indeed not new, but that's a long story.  And no,
"allocate on mmap()" is not a fix.