[PATCH] seq_path() for /proc/pid/maps

This converts /proc/pid/maps to use of seq_file, cleans the issues with
d_path() overflows as a side effect.

It's incremental to seq_path() patch.

fs/proc/base.c

@@ -322,21 +322,23 @@ static int proc_permission(struct inode *inode, int mask)
 	return proc_check_root(inode);
 }
 
-extern ssize_t proc_pid_read_maps(struct task_struct *, struct file *,
-				  char *, size_t, loff_t *);
-static ssize_t pid_maps_read(struct file * file, char * buf,
-			      size_t count, loff_t *ppos)
+extern struct seq_operations proc_pid_maps_op;
+static int maps_open(struct inode *inode, struct file *file)
 {
-	struct inode * inode = file->f_dentry->d_inode;
 	struct task_struct *task = proc_task(inode);
-	ssize_t res;
-
-	res = proc_pid_read_maps(task, file, buf, count, ppos);
-	return res;
+	int ret = seq_open(file, &proc_pid_maps_op);
+	if (!ret) {
+		struct seq_file *m = file->private_data;
+		m->private = task;
+	}
+	return ret;
 }
 
 static struct file_operations proc_maps_operations = {
-	.read		= pid_maps_read,
+	.open		= maps_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
 };
 
 extern struct seq_operations mounts_op;

fs/proc/task_mmu.c

-
 #include <linux/mm.h>
 #include <linux/hugetlb.h>
+#include <linux/seq_file.h>
 #include <asm/uaccess.h>
 
 char *task_mem(struct mm_struct *mm, char *buffer)
@@ -75,167 +75,86 @@ int task_statm(struct mm_struct *mm, int *shared, int *text,
 	return size;
 }
 
-/*
- * The way we support synthetic files > 4K
- * - without storing their contents in some buffer and
- * - without walking through the entire synthetic file until we reach the
- *   position of the requested data
- * is to cleverly encode the current position in the file's f_pos field.
- * There is no requirement that a read() call which returns `count' bytes
- * of data increases f_pos by exactly `count'.
- *
- * This idea is Linus' one. Bruno implemented it.
- */
-
-/*
- * For the /proc/<pid>/maps file, we use fixed length records, each containing
- * a single line.
- *
- * f_pos = (number of the vma in the task->mm->mmap list) * PAGE_SIZE
- *         + (index into the line)
- */
-/* for systems with sizeof(void*) == 4: */
-#define MAPS_LINE_FORMAT4	  "%08lx-%08lx %s %08lx %02x:%02x %lu"
-#define MAPS_LINE_MAX4	49 /* sum of 8  1  8  1 4 1 8 1 5 1 10 1 */
-
-/* for systems with sizeof(void*) == 8: */
-#define MAPS_LINE_FORMAT8	  "%016lx-%016lx %s %016lx %02x:%02x %lu"
-#define MAPS_LINE_MAX8	73 /* sum of 16  1  16  1 4 1 16 1 5 1 10 1 */
-
-#define MAPS_LINE_FORMAT	(sizeof(void*) == 4 ? MAPS_LINE_FORMAT4 : MAPS_LINE_FORMAT8)
-#define MAPS_LINE_MAX	(sizeof(void*) == 4 ?  MAPS_LINE_MAX4 :  MAPS_LINE_MAX8)
-
-static int proc_pid_maps_get_line (char *buf, struct vm_area_struct *map)
+static int show_map(struct seq_file *m, void *v)
 {
-	/* produce the next line */
-	char *line;
-	char str[5];
-	int flags;
-	dev_t dev;
-	unsigned long ino;
+	struct vm_area_struct *map = v;
+	struct file *file = map->vm_file;
+	int flags = map->vm_flags;
+	unsigned long ino = 0;
+	dev_t dev = 0;
 	int len;
 
-	flags = map->vm_flags;
-
-	str[0] = flags & VM_READ ? 'r' : '-';
-	str[1] = flags & VM_WRITE ? 'w' : '-';
-	str[2] = flags & VM_EXEC ? 'x' : '-';
-	str[3] = flags & VM_MAYSHARE ? 's' : 'p';
-	str[4] = 0;
-
-	dev = 0;
-	ino = 0;
-	if (map->vm_file != NULL) {
+	if (file) {
 		struct inode *inode = map->vm_file->f_dentry->d_inode;
 		dev = inode->i_sb->s_dev;
 		ino = inode->i_ino;
-		line = d_path(map->vm_file->f_dentry,
-			      map->vm_file->f_vfsmnt,
-			      buf, PAGE_SIZE);
-		buf[PAGE_SIZE-1] = '\n';
-		line -= MAPS_LINE_MAX;
-		if(line < buf)
-			line = buf;
-	} else
-		line = buf;
-
-	len = sprintf(line,
-		      MAPS_LINE_FORMAT,
-		      map->vm_start, map->vm_end, str, map->vm_pgoff << PAGE_SHIFT,
-		      MAJOR(dev), MINOR(dev), ino);
-
-	if(map->vm_file) {
-		int i;
-		for(i = len; i < MAPS_LINE_MAX; i++)
-			line[i] = ' ';
-		len = buf + PAGE_SIZE - line;
-		memmove(buf, line, len);
-	} else
-		line[len++] = '\n';
-	return len;
+	}
+
+	seq_printf(m, "%0*lx-%0*lx %c%c%c%c %0*lx %02x:%02x %lu %n",
+			2*sizeof(void*), map->vm_start,
+			2*sizeof(void*), map->vm_end,
+			flags & VM_READ ? 'r' : '-',
+			flags & VM_WRITE ? 'w' : '-',
+			flags & VM_EXEC ? 'x' : '-',
+			flags & VM_MAYSHARE ? 's' : 'p',
+			2*sizeof(void*), map->vm_pgoff << PAGE_SHIFT,
+			MAJOR(dev), MINOR(dev), ino, &len);
+
+	if (map->vm_file) {
+		len = 25 + sizeof(void*) * 6 - len;
+		if (len < 1)
+			len = 1;
+		seq_printf(m, "%*c", len, ' ');
+		seq_path(m, file->f_vfsmnt, file->f_dentry, " \t\n\\");
+	}
+	seq_putc(m, '\n');
+	return 0;
 }
 
-ssize_t proc_pid_read_maps(struct task_struct *task, struct file *file,
-			   char *buf, size_t count, loff_t *ppos)
+static void *m_start(struct seq_file *m, loff_t *pos)
 {
-	struct mm_struct *mm;
+	struct task_struct *task = m->private;
+	struct mm_struct *mm = get_task_mm(task);
 	struct vm_area_struct * map;
-	char *tmp, *kbuf;
-	long retval;
-	int off, lineno, loff;
-
-	/* reject calls with out of range parameters immediately */
-	retval = 0;
-	if (*ppos > LONG_MAX)
-		goto out;
-	if (count == 0)
-		goto out;
-	off = (long)*ppos;
-	/*
-	 * We might sleep getting the page, so get it first.
-	 */
-	retval = -ENOMEM;
-	kbuf = (char*)__get_free_page(GFP_KERNEL);
-	if (!kbuf)
-		goto out;
-
-	tmp = (char*)__get_free_page(GFP_KERNEL);
-	if (!tmp)
-		goto out_free1;
-
-	mm = get_task_mm(task);
- 
-	retval = 0;
+	loff_t l = *pos;
+
 	if (!mm)
-		goto out_free2;
+		return NULL;
 
 	down_read(&mm->mmap_sem);
 	map = mm->mmap;
-	lineno = 0;
-	loff = 0;
-	if (count > PAGE_SIZE)
-		count = PAGE_SIZE;
-	while (map) {
-		int len;
-		if (off > PAGE_SIZE) {
-			off -= PAGE_SIZE;
-			goto next;
-		}
-		len = proc_pid_maps_get_line(tmp, map);
-		len -= off;
-		if (len > 0) {
-			if (retval+len > count) {
-				/* only partial line transfer possible */
-				len = count - retval;
-				/* save the offset where the next read
-				 * must start */
-				loff = len+off;
-			}
-			memcpy(kbuf+retval, tmp+off, len);
-			retval += len;
-		}
-		off = 0;
-next:
-		if (!loff)
-			lineno++;
-		if (retval >= count)
-			break;
-		if (loff) BUG();
+	while (l-- && map)
 		map = map->vm_next;
+	if (!map) {
+		up_read(&mm->mmap_sem);
+		mmput(mm);
 	}
+	return map;
+}
+
+static void m_stop(struct seq_file *m, void *v)
+{
+	struct vm_area_struct *map = v;
+	if (map) {
+		struct mm_struct *mm = map->vm_mm;
 		up_read(&mm->mmap_sem);
 		mmput(mm);
+	}
+}
 
-	if (retval > count) BUG();
-	if (copy_to_user(buf, kbuf, retval))
-		retval = -EFAULT;
-	else
-		*ppos = (lineno << PAGE_SHIFT) + loff;
-
-out_free2:
-	free_page((unsigned long)tmp);
-out_free1:
-	free_page((unsigned long)kbuf);
-out:
-	return retval;
+static void *m_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct vm_area_struct *map = v;
+	(*pos)++;
+	if (map->vm_next)
+		return map->vm_next;
+	m_stop(m, v);
+	return NULL;
 }
+
+struct seq_operations proc_pid_maps_op = {
+	.start	= m_start,
+	.next	= m_next,
+	.stop	= m_stop,
+	.show	= show_map
+};