[PATCH] teach seq_file to discard entries

Allow ->show() return SEQ_SKIP; that will discard all
output from that element and move on.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 15 insertions, 4 deletions

diff --git a/fs/pnode.h b/fs/pnode.h
index f249be2fee7a..973c3f825e7d 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -35,4 +35,5 @@ int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,
                 struct list_head *);
 int propagate_umount(struct list_head *);
 int propagate_mount_busy(struct vfsmount *, int);
+void mnt_release_group_id(struct vfsmount *);
 #endif /* _LINUX_PNODE_H */
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 853770274f20..bf2bcfd4bcfb 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -25,6 +25,7 @@
  *      into the buffer.  In case of error ->start() and ->next() return
  *      ERR_PTR(error).  In the end of sequence they return %NULL. ->show()
  *      returns 0 in case of success and negative number in case of error.
+ *      Returning SEQ_SKIP means "discard this element and move on".
  */
 int seq_open(struct file *file, const struct seq_operations *op)
 {
@@ -114,8 +115,10 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
                 if (!p || IS_ERR(p))
                         break;
                 err = m->op->show(m, p);
-                if (err)
+                if (err < 0)
                         break;
+                if (unlikely(err))
+                        m->count = 0;
                 if (m->count < m->size)
                         goto Fill;
                 m->op->stop(m, p);
@@ -140,9 +143,10 @@ Fill:
                         break;
                 }
                 err = m->op->show(m, p);
-                if (err || m->count == m->size) {
+                if (m->count == m->size || err) {
                         m->count = offs;
-                        break;
+                        if (likely(err <= 0))
+                                break;
                 }
                 pos = next;
         }
@@ -199,8 +203,12 @@ static int traverse(struct seq_file *m, loff_t offset)
                 if (IS_ERR(p))
                         break;
                 error = m->op->show(m, p);
-                if (error)
+                if (error < 0)
                         break;
+                if (unlikely(error)) {
+                        error = 0;
+                        m->count = 0;
+                }
                 if (m->count == m->size)
                         goto Eoverflow;
                 if (pos + m->count > offset) {
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 1da1e6208a0a..d65796dc26d9 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -30,6 +30,8 @@ struct seq_operations {
         int (*show) (struct seq_file *m, void *v);
 };
 
+#define SEQ_SKIP 1
+
 int seq_open(struct file *, const struct seq_operations *);
 ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);
 loff_t seq_lseek(struct file *, loff_t, int);