Re: [PATCH] expanding truncate

[Andrew Morton <akpm@zip.com.au>]

Oleg Drokin wrote:
> 
> Hello!
> 
>     This patch makes sure that indirect pointers for holes are correctly filled in by zeroes at
>     hole-creation time. (Author is Chris Mason. fs/buffer.c part (generic_cont_expand) were written by
>     Alexander Viro)
> 
>     Please apply.
> 
> ...
> 

Please.  Do not add new library functions to the kernel with
no descriptive commentary at all.  We really need to get past
that stage.

What is this function supposed to do?  It appears that if
the page at `size' is not in cache, we write uninitialised
data into the file.


--- linux-2.4.18-pre1/fs/buffer.c.orig  Thu Jan  3 10:02:03 2002
+++ linux-2.4.18-pre1/fs/buffer.c       Thu Jan  3 10:09:24 2002
@@ -1760,6 +1760,46 @@
        return 0;
 }
 
+int generic_cont_expand(struct inode *inode, loff_t size)
+{
+       struct address_space *mapping = inode->i_mapping;
+       struct page *page;
+       unsigned long index, offset, limit;
+       int err;
+
+       limit = current->rlim[RLIMIT_FSIZE].rlim_cur;
+       if (limit != RLIM_INFINITY) {
+               if (size > limit) {
+                       send_sig(SIGXFSZ, current, 0);
+                       size = limit;
+               }
+       }
+       offset = (size & (PAGE_CACHE_SIZE-1)); /* Within page */
+
+       /* ugh.  in prepare/commit_write, if from==to==start of block, we 
+       ** skip the prepare.  make sure we never send an offset for the start
+       ** of a block
+       */
+       if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
+           offset++ ;
+       }
+       index = size >> PAGE_CACHE_SHIFT;
+       err = -ENOMEM;
+       page = grab_cache_page(mapping, index);
+       if (!page)
+               goto out;
+       err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
+       if (!err) {
+               err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+       }
+       UnlockPage(page);
+       page_cache_release(page);
+       if (err > 0)
+               err = 0;
+out:
+       return err;
+}
+