Here is a new improved blockget function, a little more general than
the one we have been using so far:
* Works for both volume metadata and file data.
* We can define whether high memory is used per, mapping, by setting
allocation mask when inode is created,
mapping_set_gfp_mask(inode->mapping, gfp_mask);
* Uses ERR_PTR return for better error reporting (need to fix the two
callers to use this).
* Returned buffer state is update if page was uptodate, dirty if page
was dirty
* Does not care about ->i_size: if we tell it to create a buffer
above i_size, it will happily do so, unlike the block library
functions. Special data transfer semantics related to ->i_size are
only for Posix file IO, which we will implement by other means that
by building the limitation into our block access functions.
* Appears SMP-safe, not tested.
* Unit tested in UML
The plan is to build our blockread on top of this in the classic
getblk/bread style, slightly improved with ERR_PTR returns. Because it
locks the page, we do not want to mix this with the block library
block_write_full_page, at least for our allocation map, because the
library function holds the page lock across the get_block -> map_region
call, which will deadlock if an allocation happens to occur on the same
page that is being written out via ->writepage.
I will post the full patch, including the in-kernel unit test, pretty
soon.
struct buffer_head *blockget(struct address_space *mapping, block_t block)
{
unsigned blockbits = ((struct inode *)mapping->host)->i_blkbits;
unsigned subshift = PAGE_CACHE_SHIFT - blockbits;
struct page *page = grab_cache_page(mapping, block >> subshift);
struct buffer_head *buffer;
if (!page)
return ERR_PTR(-ENOMEM);
if (!page_has_buffers(page))
create_empty_buffers(page, 1 << blockbits, 0);
buffer = page_buffer(page, block & ~(-1 << subshift));
get_bh(buffer);
unlock_page(page);
page_cache_release(page);
return buffer;
}
_______________________________________________
Tux3 mailing list
[email protected]
http://mailman.tux3.org/cgi-bin/mailman/listinfo/tux3
