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SubjectRe: [PATCH 1/6] seq_file: add seq_read_iter
On Sat, Nov 14, 2020 at 08:50:00PM +0000, Al Viro wrote:

OK, I think I understand what's going on. Could you check if
reverting the variant in -next and applying the following instead
fixes what you are seeing?

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 3b20e21604e7..35667112bbd1 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -168,7 +168,6 @@ EXPORT_SYMBOL(seq_read);
ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
struct seq_file *m = iocb->ki_filp->private_data;
- size_t size = iov_iter_count(iter);
size_t copied = 0;
size_t n;
void *p;
@@ -208,16 +207,15 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
}
/* if not empty - flush it first */
if (m->count) {
- n = min(m->count, size);
- if (copy_to_iter(m->buf + m->from, n, iter) != n)
- goto Efault;
+ n = copy_to_iter(m->buf + m->from, m->count, iter);
m->count -= n;
m->from += n;
- size -= n;
copied += n;
- if (!size)
- goto Done;
+ if (m->count)
+ goto Efault;
}
+ if (!iov_iter_count(iter))
+ goto Done;
/* we need at least one record in buffer */
m->from = 0;
p = m->op->start(m, &m->index);
@@ -249,6 +247,7 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
goto Done;
Fill:
/* they want more? let's try to get some more */
+ /* m->count is positive and there's space left in iter */
while (1) {
size_t offs = m->count;
loff_t pos = m->index;
@@ -263,7 +262,7 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
err = PTR_ERR(p);
break;
}
- if (m->count >= size)
+ if (m->count >= iov_iter_count(iter))
break;
err = m->op->show(m, p);
if (seq_has_overflowed(m) || err) {
@@ -273,12 +272,12 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
}
}
m->op->stop(m, p);
- n = min(m->count, size);
- if (copy_to_iter(m->buf, n, iter) != n)
- goto Efault;
+ n = copy_to_iter(m->buf, m->count, iter);
copied += n;
- m->count -= n;
m->from = n;
+ m->count -= n;
+ if (m->count)
+ goto Efault;
Done:
if (!copied)
copied = err;
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