Re: [PATCH 23/24] iomap: add support for sub-pagesize buffered I/O without buffer heads

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The problem is that we need to split extents at the eof block
so that the existing zeroing actually takes effect.  The patch below
fixes the test case for me:

diff --git a/fs/iomap.c b/fs/iomap.c
index e8f1bcdc95cf..9c88b8736de0 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -143,13 +143,20 @@ static void
 iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
 		loff_t *pos, loff_t length, unsigned *offp, unsigned *lenp)
 {
+	unsigned block_bits = inode->i_blkbits;
+	unsigned block_size = (1 << block_bits);
 	unsigned poff = *pos & (PAGE_SIZE - 1);
 	unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
+	unsigned first = poff >> block_bits;
+	unsigned last = (poff + plen - 1) >> block_bits;
+	unsigned end = (i_size_read(inode) & (PAGE_SIZE - 1)) >> block_bits;
 
+	/*
+	 * If the block size is smaller than the page size we need to check the
+	 * per-block uptodate status and adjust the offset and length if needed
+	 * to avoid reading in already uptodate ranges.
+	 */
 	if (iop) {
-		unsigned block_size = i_blocksize(inode);
-		unsigned first = poff >> inode->i_blkbits;
-		unsigned last = (poff + plen - 1) >> inode->i_blkbits;
 		unsigned int i;
 
 		/* move forward for each leading block marked uptodate */
@@ -159,17 +166,27 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
 			*pos += block_size;
 			poff += block_size;
 			plen -= block_size;
+			first++;
 		}
 
 		/* truncate len if we find any trailing uptodate block(s) */
 		for ( ; i <= last; i++) {
 			if (test_bit(i, iop->uptodate)) {
 				plen -= (last - i + 1) * block_size;
+				last = i - 1;
 				break;
 			}
 		}
 	}
 
+	/*
+	 * If the extent spans the block that contains the i_size we need to
+	 * handle both halves separately so that we properly zero data in the
+	 * page cache for blocks that are entirely outside of i_size.
+	 */
+	if (first <= end && last > end)
+		plen -= (last - end) * block_size;
+
 	*offp = poff;
 	*lenp = plen;
 }
--
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