@@ -566,34 +566,37 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
struct block_device *bdev = iocb->ki_filp->private_data;
loff_t size = bdev_nr_bytes(bdev);
- size_t count = iov_iter_count(to);
loff_t pos = iocb->ki_pos;
size_t shorted = 0;
ssize_t ret = 0;
+ size_t count;
- if (unlikely(pos + count > size)) {
+ if (unlikely(pos + iov_iter_count(to) > size)) {
if (pos >= size)
return 0;
size -= pos;
- if (count > size) {
- shorted = count - size;
- iov_iter_truncate(to, size);
- }
+ shorted = iov_iter_count(to) - size;
+ iov_iter_truncate(to, size);
}
+ count = iov_iter_count(to);
+ if (!count)
+ goto reexpand; /* skip atime */
+
if (iocb->ki_flags & IOCB_DIRECT) {
struct address_space *mapping = iocb->ki_filp->f_mapping;
if (iocb->ki_flags & IOCB_NOWAIT) {
- if (filemap_range_needs_writeback(mapping, iocb->ki_pos,
- iocb->ki_pos + count - 1))
- return -EAGAIN;
+ if (filemap_range_needs_writeback(mapping, pos,
+ pos + count - 1)) {
+ ret = -EAGAIN;
+ goto reexpand;
+ }
} else {
- ret = filemap_write_and_wait_range(mapping,
- iocb->ki_pos,
- iocb->ki_pos + count - 1);
+ ret = filemap_write_and_wait_range(mapping, pos,
+ pos + count - 1);
if (ret < 0)
- return ret;
+ goto reexpand;
}
file_accessed(iocb->ki_filp);
@@ -603,12 +606,14 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
iocb->ki_pos += ret;
count -= ret;
}
+ iov_iter_revert(to, count - iov_iter_count(to));
if (ret < 0 || !count)
- return ret;
+ goto reexpand;
}
ret = filemap_read(iocb, to, ret);
+reexpand:
if (unlikely(shorted))
iov_iter_reexpand(to, iov_iter_count(to) + shorted);
return ret;
Commit ceaa762527f4 ("block: move direct_IO into our own read_iter handler") introduced several regressions for bdev DIO: 1. read spanning EOF always returns 0 instead of the number of bytes read. This is because "count" is assigned early and isn't updated when the iterator is truncated: $ lsblk -o name,size /dev/vdb NAME SIZE vdb 1G $ xfs_io -d -c 'pread -b 4M 1021M 4M' /dev/vdb read 0/4194304 bytes at offset 1070596096 0.000000 bytes, 0 ops; 0.0007 sec (0.000000 bytes/sec and 0.0000 ops/sec) instead of $ xfs_io -d -c 'pread -b 4M 1021M 4M' /dev/vdb read 3145728/4194304 bytes at offset 1070596096 3 MiB, 1 ops; 0.0007 sec (3.865 GiB/sec and 1319.2612 ops/sec) 2. truncated iterator isn't reexpanded 3. iterator isn't reverted on blkdev_direct_IO() error 4. zero size read no longer skips atime update Fixes: ceaa762527f4 ("block: move direct_IO into our own read_iter handler") Signed-off-by: Ilya Dryomov <idryomov@gmail.com> --- block/fops.c | 33 +++++++++++++++++++-------------- 1 file changed, 19 insertions(+), 14 deletions(-)