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block: move direct_IO into our own read_iter handler 

Don't call into generic_file_read_iter() if we know it's O_DIRECT, just
set it up ourselves and call our own handler. This avoids an indirect call
for O_DIRECT.

Fall back to filemap_read() if we fail.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2021-10-28 08:57:09 -06:00
parent 4bdcd1dd4d
commit ceaa762527
1 changed files with 32 additions and 5 deletions
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37
block/fops.c
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@ -566,21 +566,48 @@ 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;
ssize_t ret = 0;
if (unlikely(pos + iov_iter_count(to) > size)) {
if (unlikely(pos + count > size)) {
if (pos >= size)
return 0;
size -= pos;
if (iov_iter_count(to) > size) {
shorted = iov_iter_count(to) - size;
if (count > size) {
shorted = count - size;
iov_iter_truncate(to, size);
}
}
ret = generic_file_read_iter(iocb, to);
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;
} else {
ret = filemap_write_and_wait_range(mapping,
iocb->ki_pos,
iocb->ki_pos + count - 1);
if (ret < 0)
return ret;
}
file_accessed(iocb->ki_filp);
ret = blkdev_direct_IO(iocb, to);
if (ret >= 0) {
iocb->ki_pos += ret;
count -= ret;
}
if (ret < 0 || !count)
return ret;
}
ret = filemap_read(iocb, to, ret);
if (unlikely(shorted))
iov_iter_reexpand(to, iov_iter_count(to) + shorted);