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nfs/localio: backfill missing partial read support for misaligned DIO 

Misaligned DIO read can be split into 3 IOs, must handle potential for
short read from each component IO (follows same pattern used for
handling partial writes, except upper layer read code handles advancing
offset before retry).

Fixes: c817248fc8 ("nfs/localio: add proper O_DIRECT support for READ and WRITE")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
This commit is contained in:
Mike Snitzer 2025-10-27 09:08:33 -04:00 committed by Anna Schumaker
parent f2060bdc21
commit d0497dd274
1 changed files with 20 additions and 4 deletions
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24
fs/nfs/localio.c
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@ -414,7 +414,7 @@ nfs_local_iters_setup_dio(struct nfs_local_kiocb *iocb, int rw,
/* Setup misaligned end?
* If so, the end is purposely setup to be issued using buffered IO
* before the middle (which will use DIO, if DIO-aligned, with AIO).
* This creates problems if/when the end results in a partial write.
* This creates problems if/when the end results in short read or write.
* So must save index and length of end to handle this corner case.
*/
if (local_dio->end_len) {
@ -580,8 +580,9 @@ static void nfs_local_read_done(struct nfs_local_kiocb *iocb)
*/
hdr->res.replen = 0;
if (hdr->res.count != hdr->args.count ||
hdr->args.offset + hdr->res.count >= i_size_read(file_inode(filp)))
/* nfs_readpage_result() handles short read */
if (hdr->args.offset + hdr->res.count >= i_size_read(file_inode(filp)))
hdr->res.eof = true;
dprintk("%s: read %ld bytes eof %d.\n", __func__,
@ -620,6 +621,7 @@ static void nfs_local_call_read(struct work_struct *work)
container_of(work, struct nfs_local_kiocb, work);
struct file *filp = iocb->kiocb.ki_filp;
const struct cred *save_cred;
bool force_done = false;
ssize_t status;
int n_iters;
@ -637,7 +639,21 @@ static void nfs_local_call_read(struct work_struct *work)
iocb->kiocb.ki_pos = iocb->offset[i];
status = filp->f_op->read_iter(&iocb->kiocb, &iocb->iters[i]);
if (status != -EIOCBQUEUED) {
if (nfs_local_pgio_done(iocb, status, false)) {
if (unlikely(status >= 0 && status < iocb->iters[i].count)) {
/* partial read */
if (i == iocb->end_iter_index) {
/* Must not account DIO partial end, otherwise (due
* to end being issued before middle): the partial
* read accounting in nfs_local_read_done()
* would incorrectly advance hdr->args.offset
*/
status = 0;
} else {
/* Partial read at start or middle, force done */
force_done = true;
}
}
if (nfs_local_pgio_done(iocb, status, force_done)) {
nfs_local_read_iocb_done(iocb);
break;
}