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> --- 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]; -- 2.17.1
