Re: [PATCH 1/6] n_tty: Start making use of -EAGAIN returned from process_output_block()
From: Andy Shevchenko <hidden>
Date: 2021-09-21 11:59:39
Also in:
linux-omap, lkml
On Tue, Sep 21, 2021 at 1:34 PM Tony Lindgren [off-list ref] wrote:
We check for -EAGAIN in n_tty_write() but never currently get it from
process_output_block(). Let's add -EAGAIN handling and break out with 0
bytes processed. Note that if we return -EAGAIN from n_tty_write(), it
will be treated as error by the caller rather than a retry.
Looking at the patch description for commit 9ef8927f45f2 ("n_tty: check
for negative and zero space return from tty_write_room") it looks like we
have not made use of -EGAIN from process_output_block() so far, so this-EGAIN?
quoted hunk ↗ jump to hunk
does not seem like it's currently needed as a fix. We can use -EAGAIN for serial layer power management changes as we now will make use of write_room() returning 0 for an idled serial port. Signed-off-by: Tony Lindgren <tony@atomide.com> --- drivers/tty/n_tty.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c@@ -549,6 +549,8 @@ static ssize_t process_output_block(struct tty_struct *tty, space = tty_write_room(tty); if (space <= 0) { mutex_unlock(&ldata->output_lock); + if (!space) + space = -EAGAIN; return space; } if (nr > space)@@ -2287,8 +2289,10 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, while (nr > 0) { ssize_t num = process_output_block(tty, b, nr); if (num < 0) { - if (num == -EAGAIN) - break; + if (num == -EAGAIN) { + retval = 0; + goto break_out; + } retval = num; goto break_out; } --2.33.0
-- With Best Regards, Andy Shevchenko