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SubjectRe: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm
On Sun, Jul 19, 2009 at 09:32:25PM -0400, Frederic Weisbecker wrote:
> On Mon, Jul 20, 2009 at 08:55:54AM +0800, Li Zefan wrote:
> > Jiri Olsa wrote:
> > > On Fri, Jul 17, 2009 at 05:37:24PM +0800, Li Zefan wrote:
> > >> Jiri Olsa wrote:
> > >>> If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> > >>> with read&write permissions, the previous setup will be removed.
> > >>>
> > >> Currently:
> > >>
> > >> # echo 'sys_open sys_close' > set_ftrace_filter
> > >> # cat set_ftrace_filter
> > >> sys_open
> > >> sys_close
> > >>
> > >> After your patch:
> > >>
> > >> # echo 'sys_open sys_close' > set_ftrace_filter
> > >> # cat set_ftrace_filter
> > >> sys_close
> > >>
> > >
> > > oops, sry I missed this..
> > >
> > > Following patch adds new FTRACE_ITER_RESET flag, as the decision needs
> > > to be taken in "open" and applied in "write". I'm not sure whats the
> > > policy for adding new flags, but it looks ok to me.
> > >
> >
> > I have no strong opinion whether to do the reset in "open" or in first
> > "write".
> >
> > All said, I think this is cleaner, without introducing a new flag:
> >
> > @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
> > return 0;
> >
> > mutex_lock(&ftrace_regex_lock);
> > + if (file->f_pos == 0 &&
> > + (file->f_mode & FMODE_WRITE) && !(file->f_flags & O_APPEND))
> > + ftrace_filter_reset(enable);
> >
> > if (file->f_mode & FMODE_READ) {
> > struct seq_file *m = file->private_data;
>
>
> Yeah, that avoids this need of creating a new flag.
> Looks like a good solution.
>

yes, but this wont work unless the *ppos value is updated instead of the
file->f_pos, because of:


SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,
size_t, count)
{
[snip]
loff_t pos = file_pos_read(file);
ret = vfs_write(file, buf, count, &pos);
file_pos_write(file, pos);
[snip]


Together with this fix I included fix for FTRACE_ITER_CONT flag, since
it does not seem to work correctly.
As far as I understand the reason for FTRACE_ITER_CONT flag is when
there's one regexp. in more write calls. I made a program to test it.

[snip]
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

int main(int argc, char **argv)
{
int fd, i;
char *file = argv[1];

if (-1 == (fd = open(file, O_WRONLY))) {
perror("open failed");
return -1;
}

for(i = 0; i < (argc - 2); i++) {
int len = strlen(argv[2+i]);
int cnt, off = 0;

while(len) {
cnt = write(fd, argv[2+i] + off, len);
len -= cnt;
off += cnt;
}
}

close(fd);
return 0;
}
[snip]

I got following behaviour on the current tip master:

sh-4.0# /tst ./set_ftrace_filter sys_o "pen "
sh-4.0# cat ./set_ftrace_filter
#### all functions enabled ####


wbr,
jirka

---
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 24e3ff5..041a327 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1616,10 +1616,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
return -ENOMEM;

mutex_lock(&ftrace_regex_lock);
- if ((file->f_mode & FMODE_WRITE) &&
- !(file->f_flags & O_APPEND))
- ftrace_filter_reset(enable);
-
if (file->f_mode & FMODE_READ) {
iter->pg = ftrace_pages_start;
iter->flags = enable ? FTRACE_ITER_FILTER :
@@ -2225,6 +2221,10 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
if (!*ppos) {
iter->flags &= ~FTRACE_ITER_CONT;
iter->buffer_idx = 0;
+
+ if ((file->f_mode & FMODE_WRITE) &&
+ !(file->f_flags & O_APPEND))
+ ftrace_filter_reset(enable);
}

ret = get_user(ch, ubuf++);
@@ -2233,7 +2233,11 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
read++;
cnt--;

- if (!(iter->flags & ~FTRACE_ITER_CONT)) {
+ /*
+ * If the parses havent finished with the last write,
+ * continue reading the user input without skipping spaces.
+ */
+ if (!(iter->flags & FTRACE_ITER_CONT)) {
/* skip white space */
while (cnt && isspace(ch)) {
ret = get_user(ch, ubuf++);
@@ -2243,8 +2247,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
cnt--;
}

+ /* only spaces were written */
if (isspace(ch)) {
- file->f_pos += read;
+ *ppos += read;
ret = read;
goto out;
}
@@ -2273,12 +2278,12 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
if (ret)
goto out;
iter->buffer_idx = 0;
- } else
+ } else {
iter->flags |= FTRACE_ITER_CONT;
+ iter->buffer[iter->buffer_idx++] = ch;
+ }

-
- file->f_pos += read;
-
+ *ppos += read;
ret = read;
out:
mutex_unlock(&ftrace_regex_lock);

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