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On Sun, 3 Sep 2000, Alexander Viro wrote:

> OK, after a bit of thinking it looks like we'll need slightly different
> prototype. How about the following? BTW, mem_is_zero() really asks for
> inclusion into string.h, IMO.

Arrgh. Sorry about that mess. Corrected variant:

diff -urN rc8-2/fs/buffer.c linux-truncate/fs/buffer.c
--- rc8-2/fs/buffer.c Sat Sep 2 21:10:37 2000
+++ linux-truncate/fs/buffer.c Sun Sep 3 11:25:34 2000
@@ -1721,6 +1721,54 @@
return 0;
}

+/*
+ * If it would be '74 that would go into libc...
+ */
+int mem_is_zero(char *p, unsigned len)
+{
+ while (len--)
+ if (*p++)
+ return 0;
+ return 1;
+}
+
+int block_zero_page(struct address_space *mapping, loff_t from, unsigned length)
+{
+ unsigned long index = from >> PAGE_CACHE_SHIFT;
+ unsigned offset = from & (PAGE_CACHE_SIZE-1);
+ struct inode *inode = (struct inode *)mapping->host;
+ struct page *page;
+ char *kaddr;
+ int err;
+
+ if (!length)
+ return 0;
+
+ page = read_cache_page(mapping, index,
+ (filler_t *)mapping->a_ops->readpage, NULL);
+ err = PTR_ERR(page);
+ if (ERR_PTR(page))
+ goto out;
+ lock_page(page);
+ err = -EIO;
+ if (!Page_Uptodate(page))
+ goto unlock;
+ kaddr = (char*)kmap(page);
+ err = 0;
+ if (mem_is_zero(kaddr+offset, length))
+ goto unmap;
+ memset(kaddr+offset, 0, length);
+ flush_dcache_page(page);
+ __block_commit_write(inode, page, offset, offset+length);
+unmap:
+ kunmap(page);
+unlock:
+ UnlockPage(page);
+ page_cache_release(page);
+out:
+ return err;
+}
+
int block_write_full_page(struct page *page, get_block_t *get_block)
{
struct inode *inode = (struct inode*)page->mapping->host;
diff -urN rc8-2/fs/ext2/inode.c linux-truncate/fs/ext2/inode.c
--- rc8-2/fs/ext2/inode.c Sun Sep 3 02:26:35 2000
+++ linux-truncate/fs/ext2/inode.c Sun Sep 3 11:39:51 2000
@@ -904,6 +904,7 @@
int nr = 0;
int n;
long iblock;
+ unsigned blocksize, tail;

if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
S_ISLNK(inode->i_mode)))
@@ -913,8 +914,13 @@

ext2_discard_prealloc(inode);

- iblock = (inode->i_size + inode->i_sb->s_blocksize-1)
+ blocksize = inode->i_sb->s_blocksize;
+ iblock = (inode->i_size + blocksize-1)
>> EXT2_BLOCK_SIZE_BITS(inode->i_sb);
+ tail = (iblock << EXT2_BLOCK_SIZE_BITS(inode->i_sb)) - inode->i_size;
+
+ if (block_zero_page(inode->i_mapping, inode->i_size, tail) != 0)
+ return;

n = ext2_block_to_path(inode, iblock, offsets);
if (n == 0)
diff -urN rc8-2/include/linux/fs.h linux-truncate/include/linux/fs.h
--- rc8-2/include/linux/fs.h Sat Sep 2 21:10:38 2000
+++ linux-truncate/include/linux/fs.h Sun Sep 3 02:20:04 2000
@@ -1162,6 +1162,7 @@

int generic_block_bmap(struct address_space *, long, get_block_t *);
int generic_commit_write(struct file *, struct page *, unsigned, unsigned);
+int block_zero_page(struct address_space *mapping, loff_t, unsigned);

extern int generic_file_mmap(struct file *, struct vm_area_struct *);
extern ssize_t generic_file_read(struct file *, char *, size_t, loff_t *);
diff -urN rc8-2/kernel/ksyms.c linux-truncate/kernel/ksyms.c
--- rc8-2/kernel/ksyms.c Sat Sep 2 21:10:39 2000
+++ linux-truncate/kernel/ksyms.c Sun Sep 3 02:20:33 2000
@@ -203,6 +203,7 @@
EXPORT_SYMBOL(block_sync_page);
EXPORT_SYMBOL(cont_prepare_write);
EXPORT_SYMBOL(generic_commit_write);
+EXPORT_SYMBOL(block_zero_page);
EXPORT_SYMBOL(generic_block_bmap);
EXPORT_SYMBOL(generic_file_read);
EXPORT_SYMBOL(do_generic_file_read);
-
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