Messages in this thread | | | Date | Tue, 11 Mar 2008 18:19:52 -0600 | From | Paul Fulghum <> | Subject | Re: [RFC][PATCH] n_tty : Loss of sync following a buffer overflow |
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Rupesh Sugathan wrote: > There seems to be a synchronization issue with the n_tty.c driver when > working in canonical mode. > The n_tty rightly discards data received following a buffer overflow and > hence the tty->read_cnt is not updated. However, the newline characters > received following a buffer overflow seems to increment the tty- > canon_data index. This may result in a loss of sync between the tty- > canon_data & tty->read_cnt while processing read in the read_chan(). > This loss of sync might be irrecoverable even when the data is later > received at a slower rate. > > ---- > I am not very sure if there is any deliberate rationale to process the > newlines even when the buffer has overflown. Please comment and review > the patch > > diff -pu a/drivers/char/n_tty.c b/drivers/char/n_tty.c
Some more information:
This is not purely theoretical. Rupesh is actually working a problem where he has seen the N_TTY buffer overflow and the canonical state variables get out of sync with read_cnt, etc.
This patch seems obviously correct, if N_TTY drops a char due to a full buffer the rest of the character processing should not take place. Particularly in this case where the extra processing leaves the tty structure in an inconsistent state.
-- Paul Fulghum Microgate Systems, Ltd
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