[PATCH] seq_file: fix condition while loop

[PATCH] seq_file: fix condition while loop

[Yi Li]

From: Yi Li <yilikernel@gmail.com>

Use the break condition of loop body.
PTR_ERR has some meanings when p is illegal,and return 0 when p is null.
set the err = 0 on the next iteration if err > 0.

Signed-off-by: Yi Li <yilikernel@gmail.com>
---
 fs/seq_file.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1600034..3796d4f 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -107,9 +107,10 @@ static int traverse(struct seq_file *m, loff_t offset)
 	}
 	p = m->op->start(m, &m->index);
 	while (p) {
-		error = PTR_ERR(p);
-		if (IS_ERR(p))
+		if (IS_ERR(p)) {
+			error = PTR_ERR(p);
 			break;
+		}
 		error = m->op->show(m, p);
 		if (error < 0)
 			break;
@@ -222,10 +223,11 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 	/* we need at least one record in buffer */
 	m->from = 0;
 	p = m->op->start(m, &m->index);
-	while (1) {
-		err = PTR_ERR(p);
-		if (!p || IS_ERR(p))
+	while (p) {
+		if (IS_ERR(p)) {
+			err = PTR_ERR(p);
 			break;
+		}
 		err = m->op->show(m, p);
 		if (err < 0)
 			break;
@@ -233,6 +235,7 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 			m->count = 0;
 		if (unlikely(!m->count)) {
 			p = m->op->next(m, p, &m->index);
+			err = 0;
 			continue;
 		}
 		if (m->count < m->size)
-- 
2.7.5

Re: [PATCH] seq_file: fix condition while loop

[Al Viro]

On Thu, Oct 31, 2019 at 07:38:21PM +0800, Yi Li wrote:
> From: Yi Li <yilikernel@gmail.com>
> 
> Use the break condition of loop body.
> PTR_ERR has some meanings when p is illegal,and return 0 when p is null.
> set the err = 0 on the next iteration if err > 0.

IDGI.  PTR_ERR() is not going to cause any kind of undefined behaviour for
any valid pointer and it's trivial to evaluate.  What's the point?

Re: [PATCH] seq_file: fix condition while loop

[李义]

On Thu, Oct 31, 2019 at 10:06 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Thu, Oct 31, 2019 at 07:38:21PM +0800, Yi Li wrote:
> > From: Yi Li <yilikernel@gmail.com>
> >
> > Use the break condition of loop body.
> > PTR_ERR has some meanings when p is illegal,and return 0 when p is null.
> > set the err = 0 on the next iteration if err > 0.
>
> IDGI.  PTR_ERR() is not going to cause any kind of undefined behaviour for
> any valid pointer and it's trivial to evaluate.  What's the point?
This patch doesn't introduce any functional changes.
Sorry for the noise..