tracing: fix splice return too large

I got these from strace:

 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 12288
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 12288
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 12288
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 16384
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 8192
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 8192
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 8192

I wanted to splice_read 4096 bytes, but it returns 8192 or larger.

It is because the return value of tracing_buffers_splice_read()
does not include "zero out any left over data" bytes.

But tracing_buffers_read() includes these bytes, we make them
consistent.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <49D46674.9030804@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9462976..1ce5dc6 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3428,7 +3428,19 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
        int size, i;
        size_t ret;
 
-       for (i = 0; i < PIPE_BUFFERS && len; i++, len -= size) {
+       if (*ppos & (PAGE_SIZE - 1)) {
+               WARN_ONCE(1, "Ftrace: previous read must page-align\n");
+               return -EINVAL;
+       }
+
+       if (len & (PAGE_SIZE - 1)) {
+               WARN_ONCE(1, "Ftrace: splice_read should page-align\n");
+               if (len < PAGE_SIZE)
+                       return -EINVAL;
+               len &= PAGE_MASK;
+       }
+
+       for (i = 0; i < PIPE_BUFFERS && len; i++, len -= PAGE_SIZE) {
                struct page *page;
                int r;
 
@@ -3467,7 +3479,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
                spd.partial[i].offset = 0;
                spd.partial[i].private = (unsigned long)ref;
                spd.nr_pages++;
-               *ppos += size;
+               *ppos += PAGE_SIZE;
        }
 
        spd.nr_pages = i;