path: root/fs/seq_file.c

// SPDX-License-Identifier: GPL-2.0
/*
 * linux/fs/seq_file.c
 *
 * helper functions for making synthetic files from sequences of records.
 * initial implementation -- AV, Oct 2001.
 */

#include <linux/fs.h>
#include <linux/export.h>
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/mm.h>
#include <linux/printk.h>
#include <linux/string_helpers.h>

#include <linux/uaccess.h>
#include <asm/page.h>

static void seq_set_overflow(struct seq_file *m)
{
	m->count = m->size;
}

static void *seq_buf_alloc(unsigned long size)
{
	return kvmalloc(size, GFP_KERNEL);
}

/**
 *	seq_open -	initialize sequential file
 *	@file: file we initialize
 *	@op: method table describing the sequence
 *
 *	seq_open() sets @file, associating it with a sequence described
 *	by @op.  @op->start() sets the iterator up and returns the first
 *	element of sequence. @op->stop() shuts it down.  @op->next()
 *	returns the next element of sequence.  @op->show() prints element
 *	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".
 *	Note: seq_open() will allocate a struct seq_file and store its
 *	pointer in @file->private_data. This pointer should not be modified.
 */
int seq_open(struct file *file, const struct seq_operations *op)
{
	struct seq_file *p;

	WARN_ON(file->private_data);

	p = kzalloc(sizeof(*p), GFP_KERNEL);
	if (!p)
		return -ENOMEM;

	file->private_data = p;

	mutex_init(&p->lock);
	p->op = op;

	// No refcounting: the lifetime of 'p' is constrained
	// to the lifetime of the file.
	p->file = file;

	/*
	 * Wrappers around seq_open(e.g. swaps_open) need to be
	 * aware of this. If they set f_version themselves, they
	 * should call seq_open first and then set f_version.
	 */
	file->f_version = 0;

	/*
	 * seq_files support lseek() and pread().  They do not implement
	 * write() at all, but we clear FMODE_PWRITE here for historical
	 * reasons.
	 *
	 * If a client of seq_files a) implements file.write() and b) wishes to
	 * support pwrite() then that client will need to implement its own
	 * file.open() which calls seq_open() and then sets FMODE_PWRITE.
	 */
	file->f_mode &= ~FMODE_PWRITE;
	return 0;
}
EXPORT_SYMBOL(seq_open);

static int traverse(struct seq_file *m, loff_t offset)
{
	loff_t pos = 0, index;
	int error = 0;
	void *p;

	m->version = 0;
	index = 0;
	m->count = m->from = 0;
	if (!offset) {
		m->index = index;
		return 0;
	}
	if (!m->buf) {
		m->buf = seq_buf_alloc(m->size = PAGE_SIZE);
		if (!m->buf)
			return -ENOMEM;
	}
	p = m->op->start(m, &index);
	while (p) {
		error = PTR_ERR(p);
		if (IS_ERR(p))
			break;
		error = m->op->show(m, p);
		if (error < 0)
			break;
		if (unlikely(error)) {
			error = 0;
			m->count = 0;
		}
		if (seq_has_overflowed(m))
			goto Eoverflow;
		if (pos + m->count > offset) {
			m->from = offset - pos;
			m->count -= m->from;
			m->index = index;
			break;
		}
		pos += m->count;
		m->count = 0;
		if (pos == offset) {
			index++;
			m->index = index;
			break;
		}
		p = m->op->next(m, p, &index);
	}
	m->op->stop(m, p);
	m->index = index;
	return error;

Eoverflow:
	m->op->stop(m, p);
	kvfree(m->buf);
	m->count = 0;
	m->buf = seq_buf_alloc(m->size <<= 1);
	return !m->buf ? -ENOMEM : -EAGAIN;
}

/**
 *	seq_read -	->read() method for sequential files.
 *	@file: the file to read from
 *	@buf: the buffer to read to
 *	@size: the maximum number of bytes to read
 *	@ppos: the current position in the file
 *
 *	Ready-made ->f_op->read()
 */
ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
	struct seq_file *m = file->private_data;
	size_t copied = 0;
	loff_t pos;
	size_t n;
	void *p;
	int err = 0;

	mutex_lock(&m->lock);

	/*
	 * seq_file->op->..m_start/m_stop/m_next may do special actions
	 * or optimisations based on the file->f_version, so we want to
	 * pass the file->f_version to those methods.
	 *
	 * seq_file->version is just copy of f_version, and seq_file
	 * methods can treat it simply as file version.
	 * It is copied in first and copied out after all operations.
	 * It is convenient to have it as  part of structure to avoid the
	 * need of passing another argument to all the seq_file methods.
	 */
	m->version = file->f_version;

	/*
	 * if request is to read from zero offset, reset iterator to first
	 * record as it might have been already advanced by previous requests
	 */
	if (*ppos == 0)
		m->index = 0;

	/* Don't assume *ppos is where we left it */
	if (unlikely(*ppos != m->read_pos)) {
		while ((err = traverse(m, *ppos)) == -EAGAIN)
			;
		if (err) {
			/* With prejudice... */
			m->read_pos = 0;
			m->version = 0;
			m->index = 0;
			m->count = 0;
			goto Done;
		} else {
			m