linux-kernel - Re: [PATCH v4 6/6] io_uring: add support for zone-append

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Date:   Fri, 31 Jul 2020 14:08:02 +0100
From:   "hch@...radead.org" <hch@...radead.org>
To:     Damien Le Moal <Damien.LeMoal@....com>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        Kanchan Joshi <joshiiitr@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        Kanchan Joshi <joshi.k@...sung.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "bcrl@...ck.org" <bcrl@...ck.org>,
        Matthew Wilcox <willy@...radead.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-aio@...ck.org" <linux-aio@...ck.org>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        SelvaKumar S <selvakuma.s1@...sung.com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>,
        Johannes Thumshirn <Johannes.Thumshirn@....com>,
        Naohiro Aota <Naohiro.Aota@....com>
Subject: Re: [PATCH v4 6/6] io_uring: add support for zone-append

And FYI, this is what I'd do for a hacky aio-only prototype (untested):


diff --git a/fs/aio.c b/fs/aio.c
index 91e7cc4a9f179b..42b1934e38758b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1438,7 +1438,10 @@ static void aio_complete_rw(struct kiocb *kiocb, long res, long res2)
 	}
 
 	iocb->ki_res.res = res;
-	iocb->ki_res.res2 = res2;
+	if ((kiocb->ki_flags & IOCB_REPORT_OFFSET) && res > 0)
+		iocb->ki_res.res2 = kiocb->ki_pos - res;
+	else
+		iocb->ki_res.res2 = res2;
 	iocb_put(iocb);
 }
 
@@ -1452,6 +1455,8 @@ static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
 	req->ki_flags = iocb_flags(req->ki_filp);
 	if (iocb->aio_flags & IOCB_FLAG_RESFD)
 		req->ki_flags |= IOCB_EVENTFD;
+	if (iocb->aio_flags & IOCB_FLAG_REPORT_OFFSET)
+		req->ki_flags |= IOCB_REPORT_OFFSET;
 	req->ki_hint = ki_hint_validate(file_write_hint(req->ki_filp));
 	if (iocb->aio_flags & IOCB_FLAG_IOPRIO) {
 		/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f5abba86107d86..522b0a3437d420 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -316,6 +316,7 @@ enum rw_hint {
 #define IOCB_WRITE		(1 << 6)
 #define IOCB_NOWAIT		(1 << 7)
 #define IOCB_NOIO		(1 << 9)
+#define IOCB_REPORT_OFFSET	(1 << 10)
 
 struct kiocb {
 	struct file		*ki_filp;
diff --git a/include/uapi/linux/aio_abi.h b/include/uapi/linux/aio_abi.h
index 8387e0af0f768a..e4313d7aa3b7e7 100644
--- a/include/uapi/linux/aio_abi.h
+++ b/include/uapi/linux/aio_abi.h
@@ -55,6 +55,7 @@ enum {
  */
 #define IOCB_FLAG_RESFD		(1 << 0)
 #define IOCB_FLAG_IOPRIO	(1 << 1)
+#define IOCB_FLAG_REPORT_OFFSET	(1 << 2)
 
 /* read() from /dev/aio returns these structures. */
 struct io_event {