On Thu, 21 Jan 2021, Denis Efremov wrote:

I think it's hard to recall the exact reasons after so many years. 

Yeah, I guess so :)

I'll send a patch today based on this one.

I am currently waiting for confirmation by the original reporter that the 
patch below fixes the issue.



From: Jiri Kosina <redacted>
Subject: [PATCH] floppy: reintroduce O_NDELAY fix

Originally fixed in 09954bad4 ("floppy: refactor open() flags handling")
then reverted for unknown reason in f2791e7eadf437 instead of taking
the open(O_ACCMODE) for ioctl-only open fix, which had the changelog below

====
Commit 09954bad4 ("floppy: refactor open() flags handling"), as a
side-effect, causes open(/dev/fdX, O_ACCMODE) to fail. It turns out that
this is being used setfdprm userspace for ioctl-only open().

Reintroduce back the original behavior wrt !(FMODE_READ|FMODE_WRITE)
modes, while still keeping the original O_NDELAY bug fixed.

Cc: stable@vger.kernel.org # v4.5+
Reported-by: Wim Osterholt <redacted>
Tested-by: Wim Osterholt <redacted>
Signed-off-by: Jiri Kosina <redacted>
=====

Fixes: 09954bad4 ("floppy: refactor open() flags handling")
Fixes: f2791e7ead ("Revert "floppy: refactor open() flags handling"")
Signed-off-by: Jiri Kosina <redacted>
---
 drivers/block/floppy.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index dfe1dfc901cc..bda9417aa0a8 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c

@@ -4121,23 +4121,22 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
 	if (fdc_state[FDC(drive)].rawcmd == 1)
 		fdc_state[FDC(drive)].rawcmd = 2;
 
-	if (!(mode & FMODE_NDELAY)) {
-		if (mode & (FMODE_READ|FMODE_WRITE)) {
-			drive_state[drive].last_checked = 0;
-			clear_bit(FD_OPEN_SHOULD_FAIL_BIT,
-				  &drive_state[drive].flags);
-			if (bdev_check_media_change(bdev))
-				floppy_revalidate(bdev->bd_disk);
-			if (test_bit(FD_DISK_CHANGED_BIT, &drive_state[drive].flags))
-				goto out;
-			if (test_bit(FD_OPEN_SHOULD_FAIL_BIT, &drive_state[drive].flags))
-				goto out;
-		}
-		res = -EROFS;
-		if ((mode & FMODE_WRITE) &&
-		    !test_bit(FD_DISK_WRITABLE_BIT, &drive_state[drive].flags))
+	if (mode & (FMODE_READ|FMODE_WRITE)) {
+		UDRS->last_checked = 0;
+		clear_bit(FD_OPEN_SHOULD_FAIL_BIT, &drive_state[drive].flags);
+		check_disk_change(bdev);
+		if (test_bit(FD_DISK_CHANGED_BIT, &drive_state[drive].flags))
+			goto out;
+		if (test_bit(FD_OPEN_SHOULD_FAIL_BIT, &drive_state[drive].flags))
 			goto out;
 	}
+
+	res = -EROFS;
+
+	if ((mode & FMODE_WRITE) &&
+			!test_bit(FD_DISK_WRITABLE_BIT, &drive_state[drive].flags))
+		goto out;
+
 	mutex_unlock(&open_lock);
 	mutex_unlock(&floppy_mutex);
 	return 0;

-- 
Jiri Kosina
SUSE Labs