uml: fix console writing bugs
The previous console cleanup patch switched generic_read and generic_write from calling os_{read,write}_file to calling read and write directly. Because the calling convention is different, they now need to get any error from errno rather than the return value. I did this for generic_read, but forgot about generic_write. While chasing some output corruption, I noticed that line_write was unnecessarily calling flush_buffer, and deleted it. I don't understand why, but the corruption disappeared. This is unneeded because there already is a perfectly good mechanism for finding out when the host output device has some room to write data - there is an interrupt that comes in when writes can happen again. line_write calling flush_buffer seemed to just be an attempt to opportunistically get some data out to the host. I also made write_chan short-circuit calling into the host-level code for zero-length writes. Calling libc write with a length of zero conflated write not being able to write anything with asking it not to write anything. Better to just cut it off as soon as possible. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -291,6 +291,9 @@ int write_chan(struct list_head *chans, const char *buf, int len,
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struct chan *chan = NULL;
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int n, ret = 0;
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if (len == 0)
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return 0;
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list_for_each(ele, chans) {
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chan = list_entry(ele, struct chan, list);
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if (!chan->output || (chan->ops->write == NULL))
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@ -38,7 +38,16 @@ int generic_read(int fd, char *c_out, void *unused)
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int generic_write(int fd, const char *buf, int n, void *unused)
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{
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return write(fd, buf, n);
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int err;
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err = write(fd, buf, n);
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if (err > 0)
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return err;
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else if (errno == EAGAIN)
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return 0;
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else if (err == 0)
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return -EIO;
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return -errno;
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}
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int generic_window_size(int fd, void *unused, unsigned short *rows_out,
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@ -216,18 +216,15 @@ int line_write(struct tty_struct *tty, const unsigned char *buf, int len)
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{
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struct line *line = tty->driver_data;
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unsigned long flags;
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int n, err, ret = 0;
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int n, ret = 0;
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if(tty->stopped)
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return 0;
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spin_lock_irqsave(&line->lock, flags);
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if (line->head != line->tail) {
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if (line->head != line->tail)
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ret = buffer_data(line, buf, len);
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err = flush_buffer(line);
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if (err <= 0 && (err != -EAGAIN || !ret))
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ret = err;
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} else {
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else {
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n = write_chan(&line->chan_list, buf, len,
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line->driver->write_irq);
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if (n < 0) {
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