[PATCH] seq_path(), /proc/mounts and /proc/swaps

This adds a new seq_...() helper:

   seq_path(seq_file, mnt, dentry, escape)

It spits the pathname into seq_file, does octal escapes for given set of
characters, returns the number of characters it'd produced or -1 in case
of error.  Long names are handled gracefully - you don't need anything
to do, generic seq_file logics will do the right thing.

/proc/mounts and /proc/swaps are converted to use of seq_path(), some
junk removed.

/proc/pid/maps will be converted next.

fs/dcache.c

@@ -1275,7 +1275,7 @@ void d_move(struct dentry * dentry, struct dentry * target)
  * the string " (deleted)" is appended. Note that this is ambiguous. Returns
  * the buffer.
  *
- * "buflen" should be %PAGE_SIZE or more. Caller holds the dcache_lock.
+ * "buflen" should be positive. Caller holds the dcache_lock.
  */
 static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
 			struct dentry *root, struct vfsmount *rootmnt,
@@ -1290,9 +1290,13 @@ static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
 	if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
 		buflen -= 10;
 		end -= 10;
+		if (buflen < 0)
+			goto Elong;
 		memcpy(end, " (deleted)", 10);
 	}
 
+	if (buflen < 1)
+		goto Elong;
 	/* Get '/' right */
 	retval = end-1;
 	*retval = '/';
@@ -1315,7 +1319,7 @@ static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
 		namelen = dentry->d_name.len;
 		buflen -= namelen + 1;
 		if (buflen < 0)
-			return ERR_PTR(-ENAMETOOLONG);
+			goto Elong;
 		end -= namelen;
 		memcpy(end, dentry->d_name.name, namelen);
 		*--end = '/';
@@ -1328,12 +1332,13 @@ static char * __d_path( struct dentry *dentry, struct vfsmount *vfsmnt,
 global_root:
 	namelen = dentry->d_name.len;
 	buflen -= namelen;
-	if (buflen >= 0) {
+	if (buflen < 0)
+		goto Elong;
 	retval -= namelen-1;	/* hit the slash */
 	memcpy(retval, dentry->d_name.name, namelen);
-	} else
-		retval = ERR_PTR(-ENAMETOOLONG);
 	return retval;
+Elong:
+	return ERR_PTR(-ENAMETOOLONG);
 }
 
 /* write full pathname into buffer and return start of pathname */

fs/namespace.c

@@ -211,19 +211,10 @@ static int show_vfsmnt(struct seq_file *m, void *v)
 		{ 0, NULL }
 	};
 	struct proc_fs_info *fs_infop;
-	char *path_buf, *path;
-
-	path_buf = (char *) __get_free_page(GFP_KERNEL);
-	if (!path_buf)
-		return -ENOMEM;
-	path = d_path(mnt->mnt_root, mnt, path_buf, PAGE_SIZE);
-	if (IS_ERR(path))
-		path = " (too long)";
 
 	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
 	seq_putc(m, ' ');
-	mangle(m, path);
-	free_page((unsigned long) path_buf);
+	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
 	seq_putc(m, ' ');
 	mangle(m, mnt->mnt_sb->s_type->name);
 	seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");

fs/seq_file.c

@@ -297,6 +297,37 @@ int seq_printf(struct seq_file *m, const char *f, ...)
 	return -1;
 }
 
+int seq_path(struct seq_file *m,
+		struct vfsmount *mnt, struct dentry *dentry,
+		char *esc)
+{
+	if (m->count < m->size) {
+		char *s = m->buf + m->count;
+		char *p = d_path(dentry, mnt, s, m->size - m->count);
+		if (!IS_ERR(p)) {
+			while (s <= p) {
+				char c = *p++;
+				if (!c) {
+					p = m->buf + m->count;
+					m->count = s - m->buf;
+					return s - p;
+				} else if (!strchr(esc, c)) {
+					*s++ = c;
+				} else if (s + 4 > p) {
+					break;
+				} else {
+					*s++ = '\\';
+					*s++ = '0' + ((c & 0300) >> 6);
+					*s++ = '0' + ((c & 070) >> 3);
+					*s++ = '0' + (c & 07);
+				}
+			}
+		}
+	}
+	m->count = m->size;
+	return -1;
+}
+
 static void *single_start(struct seq_file *p, loff_t *pos)
 {
 	return NULL + (*pos == 0);

include/linux/seq_file.h

@@ -8,6 +8,8 @@
 
 struct seq_operations;
 struct file;
+struct vfsmount;
+struct dentry;
 struct inode;
 
 struct seq_file {
@@ -58,6 +60,8 @@ static inline int seq_puts(struct seq_file *m, const char *s)
 int seq_printf(struct seq_file *, const char *, ...)
 	__attribute__ ((format (printf,2,3)));
 
+int seq_path(struct seq_file *, struct vfsmount *, struct dentry *, char *);
+
 int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
 int single_release(struct inode *, struct file *);
 int seq_release_private(struct inode *, struct file *);

mm/swapfile.c

@@ -1118,14 +1118,9 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
 	struct swap_info_struct *ptr = swap_info;
 	int i;
 	loff_t l = *pos;
-	char * page = (char *) __get_free_page(GFP_KERNEL);
 
-	swap->private = page;	/* save for swap_show */
 	swap_list_lock();
 
-	if (!page)
-		return ERR_PTR(-ENOMEM);
-
 	for (i = 0; i < nr_swapfiles; i++, ptr++) {
 		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
 			continue;
@@ -1154,24 +1149,21 @@ static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
 static void swap_stop(struct seq_file *swap, void *v)
 {
 	swap_list_unlock();
-	free_page((unsigned long) swap->private);
-	swap->private = NULL;
 }
 
 static int swap_show(struct seq_file *swap, void *v)
 {
 	struct swap_info_struct *ptr = v;
 	struct file *file;
-	char *path;
+	int len;
 
 	if (v == swap_info)
 		seq_puts(swap, "Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
 
 	file = ptr->swap_file;
-	path = d_path(file->f_dentry, file->f_vfsmnt, swap->private, PAGE_SIZE);
-
-	seq_printf(swap, "%-39s %s\t%d\t%ld\t%d\n",
-		       path,
+	len = seq_path(swap, file->f_vfsmnt, file->f_dentry, " \t\n\\");
+	seq_printf(swap, "%*s %s\t%d\t%ld\t%d\n",
+		       len < 40 ? 40 - len : 1, " ",
 		       S_ISBLK(file->f_dentry->d_inode->i_mode) ?
 				"partition" : "file\t",
 		       ptr->pages << (PAGE_SHIFT - 10),