On 2019-09-24, <zhe.he@xxxxxxxxxxxxx> wrote: > From: He Zhe <zhe.he@xxxxxxxxxxxxx> > > When user-space wants to read the first message, that is when user->seq > is 0, and that message has gone, it currently automatically resets > user->seq to current first seq. This mis-aligns with mainline kernel. > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/dev-kmsg#n39 > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/printk/printk.c#n899 > > We should inform user-space that what it wants has gone by returning EPIPE > in such scenario. > > Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx> Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx> > --- > kernel/printk/printk.c | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index e3fa33f2e23c..58c545a528b3 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -703,14 +703,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, > goto out; > } > > - if (user->seq == 0) { > - user->seq = seq; > - } else { > - user->seq++; > - if (user->seq < seq) { > - ret = -EPIPE; > - goto restore_out; > - } > + user->seq++; > + if (user->seq < seq) { > + ret = -EPIPE; > + goto restore_out; > } > > msg = (struct printk_log *)&user->msgbuf[0];
