vfs: seq_file: add helpers for data filling
Miklos Szeredi [Mon, 21 Sep 2009 12:48:36 +0000 (14:48 +0200)]
Add two helpers that allow access to the seq_file's own buffer, but
hide the internal details of seq_files.

This allows easier implementation of special purpose filling
functions.  It also cleans up some existing functions which duplicated
the seq_file logic.

Make these inline functions in seq_file.h, as suggested by Al.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/seq_file.c
include/linux/seq_file.h

index 66efd0a..eae7d9d 100644 (file)
@@ -429,20 +429,21 @@ EXPORT_SYMBOL(mangle_path);
  */
 int seq_path(struct seq_file *m, struct path *path, char *esc)
 {
-       if (m->count < m->size) {
-               char *s = m->buf + m->count;
-               char *p = d_path(path, s, m->size - m->count);
+       char *buf;
+       size_t size = seq_get_buf(m, &buf);
+       int res = -1;
+
+       if (size) {
+               char *p = d_path(path, buf, size);
                if (!IS_ERR(p)) {
-                       s = mangle_path(s, p, esc);
-                       if (s) {
-                               p = m->buf + m->count;
-                               m->count = s - m->buf;
-                               return s - p;
-                       }
+                       char *end = mangle_path(buf, p, esc);
+                       if (end)
+                               res = end - buf;
                }
        }
-       m->count = m->size;
-       return -1;
+       seq_commit(m, res);
+
+       return res;
 }
 EXPORT_SYMBOL(seq_path);
 
@@ -454,27 +455,28 @@ EXPORT_SYMBOL(seq_path);
 int seq_path_root(struct seq_file *m, struct path *path, struct path *root,
                  char *esc)
 {
-       int err = -ENAMETOOLONG;
-       if (m->count < m->size) {
-               char *s = m->buf + m->count;
+       char *buf;
+       size_t size = seq_get_buf(m, &buf);
+       int res = -ENAMETOOLONG;
+
+       if (size) {
                char *p;
 
                spin_lock(&dcache_lock);
-               p = __d_path(path, root, s, m->size - m->count);
+               p = __d_path(path, root, buf, size);
                spin_unlock(&dcache_lock);
-               err = PTR_ERR(p);
+               res = PTR_ERR(p);
                if (!IS_ERR(p)) {
-                       s = mangle_path(s, p, esc);
-                       if (s) {
-                               p = m->buf + m->count;
-                               m->count = s - m->buf;
-                               return 0;
-                       }
-                       err = -ENAMETOOLONG;
+                       char *end = mangle_path(buf, p, esc);
+                       if (end)
+                               res = end - buf;
+                       else
+                               res = -ENAMETOOLONG;
                }
        }
-       m->count = m->size;
-       return err;
+       seq_commit(m, res);
+
+       return res < 0 ? res : 0;
 }
 
 /*
@@ -482,20 +484,21 @@ int seq_path_root(struct seq_file *m, struct path *path, struct path *root,
  */
 int seq_dentry(struct seq_file *m, struct dentry *dentry, char *esc)
 {
-       if (m->count < m->size) {
-               char *s = m->buf + m->count;
-               char *p = dentry_path(dentry, s, m->size - m->count);
+       char *buf;
+       size_t size = seq_get_buf(m, &buf);
+       int res = -1;
+
+       if (size) {
+               char *p = dentry_path(dentry, buf, size);
                if (!IS_ERR(p)) {
-                       s = mangle_path(s, p, esc);
-                       if (s) {
-                               p = m->buf + m->count;
-                               m->count = s - m->buf;
-                               return s - p;
-                       }
+                       char *end = mangle_path(buf, p, esc);
+                       if (end)
+                               res = end - buf;
                }
        }
-       m->count = m->size;
-       return -1;
+       seq_commit(m, res);
+
+       return res;
 }
 
 int seq_bitmap(struct seq_file *m, const unsigned long *bits,
index 0c6a86b..8366d8f 100644 (file)
@@ -35,6 +35,44 @@ struct seq_operations {
 
 #define SEQ_SKIP 1
 
+/**
+ * seq_get_buf - get buffer to write arbitrary data to
+ * @m: the seq_file handle
+ * @bufp: the beginning of the buffer is stored here
+ *
+ * Return the number of bytes available in the buffer, or zero if
+ * there's no space.
+ */
+static inline size_t seq_get_buf(struct seq_file *m, char **bufp)
+{
+       BUG_ON(m->count > m->size);
+       if (m->count < m->size)
+               *bufp = m->buf + m->count;
+       else
+               *bufp = NULL;
+
+       return m->size - m->count;
+}
+
+/**
+ * seq_commit - commit data to the buffer
+ * @m: the seq_file handle
+ * @num: the number of bytes to commit
+ *
+ * Commit @num bytes of data written to a buffer previously acquired
+ * by seq_buf_get.  To signal an error condition, or that the data
+ * didn't fit in the available space, pass a negative @num value.
+ */
+static inline void seq_commit(struct seq_file *m, int num)
+{
+       if (num < 0) {
+               m->count = m->size;
+       } else {
+               BUG_ON(m->count + num > m->size);
+               m->count += num;
+       }
+}
+
 char *mangle_path(char *s, char *p, char *esc);
 int seq_open(struct file *, const struct seq_operations *);
 ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);