// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2011-2020 Junjiro R. Okajima
 */

/*
 * File-based Hierarchy Storage Management
 */

#include <linux/anon_inodes.h>
#include <linux/poll.h>
#include <linux/seq_file.h>
#include <linux/statfs.h>
#include "aufs.h"

static aufs_bindex_t au_fhsm_bottom(struct super_block *sb)
{
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;

	SiMustAnyLock(sb);

	sbinfo = au_sbi(sb);
	fhsm = &sbinfo->si_fhsm;
	AuDebugOn(!fhsm);
	return fhsm->fhsm_bottom;
}

void au_fhsm_set_bottom(struct super_block *sb, aufs_bindex_t bindex)
{
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;

	SiMustWriteLock(sb);

	sbinfo = au_sbi(sb);
	fhsm = &sbinfo->si_fhsm;
	AuDebugOn(!fhsm);
	fhsm->fhsm_bottom = bindex;
}

/* ---------------------------------------------------------------------- */

static int au_fhsm_test_jiffy(struct au_sbinfo *sbinfo, struct au_branch *br)
{
	struct au_br_fhsm *bf;

	bf = br->br_fhsm;
	MtxMustLock(&bf->bf_lock);

	return !bf->bf_readable
		|| time_after(jiffies,
			      bf->bf_jiffy + sbinfo->si_fhsm.fhsm_expire);
}

/* ---------------------------------------------------------------------- */

static void au_fhsm_notify(struct super_block *sb, int val)
{
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;

	SiMustAnyLock(sb);

	sbinfo = au_sbi(sb);
	fhsm = &sbinfo->si_fhsm;
	if (au_fhsm_pid(fhsm)
	    && atomic_read(&fhsm->fhsm_readable) != -1) {
		atomic_set(&fhsm->fhsm_readable, val);
		if (val)
			wake_up(&fhsm->fhsm_wqh);
	}
}

static int au_fhsm_stfs(struct super_block *sb, aufs_bindex_t bindex,
			struct aufs_stfs *rstfs, int do_lock, int do_notify)
{
	int err;
	struct au_branch *br;
	struct au_br_fhsm *bf;

	br = au_sbr(sb, bindex);
	AuDebugOn(au_br_rdonly(br));
	bf = br->br_fhsm;
	AuDebugOn(!bf);

	if (do_lock)
		mutex_lock(&bf->bf_lock);
	else
		MtxMustLock(&bf->bf_lock);

	/* sb->s_root for NFS is unreliable */
	err = au_br_stfs(br, &bf->bf_stfs);
	if (unlikely(err)) {
		AuErr1("FHSM failed (%d), b%d, ignored.\n", bindex, err);
		goto out;
	}

	bf->bf_jiffy = jiffies;
	bf->bf_readable = 1;
	if (do_notify)
		au_fhsm_notify(sb, /*val*/1);
	if (rstfs)
		*rstfs = bf->bf_stfs;

out:
	if (do_lock)
		mutex_unlock(&bf->bf_lock);
	au_fhsm_notify(sb, /*val*/1);

	return err;
}

void au_fhsm_wrote(struct super_block *sb, aufs_bindex_t bindex, int force)
{
	int err;
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;
	struct au_branch *br;
	struct au_br_fhsm *bf;

	AuDbg("b%d, force %d\n", bindex, force);
	SiMustAnyLock(sb);

	sbinfo = au_sbi(sb);
	fhsm = &sbinfo->si_fhsm;
	if (!au_ftest_si(sbinfo, FHSM)
	    || fhsm->fhsm_bottom == bindex)
		return;

	br = au_sbr(sb, bindex);
	bf = br->br_fhsm;
	AuDebugOn(!bf);
	mutex_lock(&bf->bf_lock);
	if (force
	    || au_fhsm_pid(fhsm)
	    || au_fhsm_test_jiffy(sbinfo, br))
		err = au_fhsm_stfs(sb, bindex, /*rstfs*/NULL, /*do_lock*/0,
				  /*do_notify*/1);
	mutex_unlock(&bf->bf_lock);
}

void au_fhsm_wrote_all(struct super_block *sb, int force)
{
	aufs_bindex_t bindex, bbot;
	struct au_branch *br;

	/* exclude the bottom */
	bbot = au_fhsm_bottom(sb);
	for (bindex = 0; bindex < bbot; bindex++) {
		br = au_sbr(sb, bindex);
		if (au_br_fhsm(br->br_perm))
			au_fhsm_wrote(sb, bindex, force);
	}
}

/* ---------------------------------------------------------------------- */

static __poll_t au_fhsm_poll(struct file *file, struct poll_table_struct *wait)
{
	__poll_t mask;
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;

	mask = 0;
	sbinfo = file->private_data;
	fhsm = &sbinfo->si_fhsm;
	poll_wait(file, &fhsm->fhsm_wqh, wait);
	if (atomic_read(&fhsm->fhsm_readable))
		mask = EPOLLIN /* | EPOLLRDNORM */;

	if (!mask)
		AuDbg("mask 0x%x\n", mask);
	return mask;
}

static int au_fhsm_do_read_one(struct aufs_stbr __user *stbr,
			      struct aufs_stfs *stfs, __s16 brid)
{
	int err;

	err = copy_to_user(&stbr->stfs, stfs, sizeof(*stfs));
	if (!err)
		err = __put_user(brid, &stbr->brid);
	if (unlikely(err))
		err = -EFAULT;

	return err;
}

static ssize_t au_fhsm_do_read(struct super_block *sb,
			       struct aufs_stbr __user *stbr, size_t count)
{
	ssize_t err;
	int nstbr;
	aufs_bindex_t bindex, bbot;
	struct au_branch *br;
	struct au_br_fhsm *bf;

	/* except the bottom branch */
	err = 0;
	nstbr = 0;
	bbot = au_fhsm_bottom(sb);
	for (bindex = 0; !err && bindex < bbot; bindex++) {
		br = au_sbr(sb, bindex);
		if (!au_br_fhsm(br->br_perm))
			continue;

		bf = br->br_fhsm;
		mutex_lock(&bf->bf_lock);
		if (bf->bf_readable) {
			err = -EFAULT;
			if (count >= sizeof(*stbr))
				err = au_fhsm_do_read_one(stbr++, &bf->bf_stfs,
							  br->br_id);
			if (!err) {
				bf->bf_readable = 0;
				count -= sizeof(*stbr);
				nstbr++;
			}
		}
		mutex_unlock(&bf->bf_lock);
	}
	if (!err)
		err = sizeof(*stbr) * nstbr;

	return err;
}

static ssize_t au_fhsm_read(struct file *file, char __user *buf, size_t count,
			   loff_t *pos)
{
	ssize_t err;
	int readable;
	aufs_bindex_t nfhsm, bindex, bbot;
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;
	struct au_branch *br;
	struct super_block *sb;

	err = 0;
	sbinfo = file->private_data;
	fhsm = &sbinfo->si_fhsm;
need_data:
	spin_lock_irq(&fhsm->fhsm_wqh.lock);
	if (!atomic_read(&fhsm->fhsm_readable)) {
		if (vfsub_file_flags(file) & O_NONBLOCK)
			err = -EAGAIN;
		else
			err = wait_event_interruptible_locked_irq
				(fhsm->fhsm_wqh,
				 atomic_read(&fhsm->fhsm_readable));
	}
	spin_unlock_irq(&fhsm->fhsm_wqh.lock);
	if (unlikely(err))
		goto out;

	/* sb may already be dead */
	au_rw_read_lock(&sbinfo->si_rwsem);
	readable = atomic_read(&fhsm->fhsm_readable);
	if (readable > 0) {
		sb = sbinfo->si_sb;
		AuDebugOn(!sb);
		/* exclude the bottom branch */
		nfhsm = 0;
		bbot = au_fhsm_bottom(sb);
		for (bindex = 0; bindex < bbot; bindex++) {
			br = au_sbr(sb, bindex);
			if (au_br_fhsm(br->br_perm))
				nfhsm++;
		}
		err = -EMSGSIZE;
		if (nfhsm * sizeof(struct aufs_stbr) <= count) {
			atomic_set(&fhsm->fhsm_readable, 0);
			err = au_fhsm_do_read(sbinfo->si_sb, (void __user *)buf,
					     count);
		}
	}
	au_rw_read_unlock(&sbinfo->si_rwsem);
	if (!readable)
		goto need_data;

out:
	return err;
}

static int au_fhsm_release(struct inode *inode, struct file *file)
{
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;

	/* sb may already be dead */
	sbinfo = file->private_data;
	fhsm = &sbinfo->si_fhsm;
	spin_lock(&fhsm->fhsm_spin);
	fhsm->fhsm_pid = 0;
	spin_unlock(&fhsm->fhsm_spin);
	kobject_put(&sbinfo->si_kobj);

	return 0;
}

static const struct file_operations au_fhsm_fops = {
	.owner		= THIS_MODULE,
	.llseek		= noop_llseek,
	.read		= au_fhsm_read,
	.poll		= au_fhsm_poll,
	.release	= au_fhsm_release
};

int au_fhsm_fd(struct super_block *sb, int oflags)
{
	int err, fd;
	struct au_sbinfo *sbinfo;
	struct au_fhsm *fhsm;

	err = -EPERM;
	if (unlikely(!capable(CAP_SYS_ADMIN)))
		goto out;

	err = -EINVAL;
	if (unlikely(oflags & ~(O_CLOEXEC | O_NONBLOCK)))
		goto out;

	err = 0;
	sbinfo = au_sbi(sb);
	fhsm = &sbinfo->si_fhsm;
	spin_lock(&fhsm->fhsm_spin);
	if (!fhsm->fhsm_pid)
		fhsm->fhsm_pid = current->pid;
	else
		err = -EBUSY;
	spin_unlock(&fhsm->fhsm_spin);
	if (unlikely(err))
		goto out;

	oflags |= O_RDONLY;
	/* oflags |= FMODE_NONOTIFY; */
	fd = anon_inode_getfd("[aufs_fhsm]", &au_fhsm_fops, sbinfo, oflags);
	err = fd;
	if (unlikely(fd < 0))
		goto out_pid;

	/* succeed regardless 'fhsm' status */
	kobject_get(&sbinfo->si_kobj);
	si_noflush_read_lock(sb);
	if (au_ftest_si(sbinfo, FHSM))
		au_fhsm_wrote_all(sb, /*force*/0);
	si_read_unlock(sb);
	goto out; /* success */

out_pid:
	spin_lock(&fhsm->fhsm_spin);
	fhsm->fhsm_pid = 0;
	spin_unlock(&fhsm->fhsm_spin);
out:
	AuTraceErr(err);
	return err;
}

/* ---------------------------------------------------------------------- */

int au_fhsm_br_alloc(struct au_branch *br)
{
	int err;

	err = 0;
	br->br_fhsm = kmalloc(sizeof(*br->br_fhsm), GFP_NOFS);
	if (br->br_fhsm)
		au_br_fhsm_init(br->br_fhsm);
	else
		err = -ENOMEM;

	return err;
}

/* ---------------------------------------------------------------------- */

void au_fhsm_fin(struct super_block *sb)
{
	au_fhsm_notify(sb, /*val*/-1);
}

void au_fhsm_init(struct au_sbinfo *sbinfo)
{
	struct au_fhsm *fhsm;

	fhsm = &sbinfo->si_fhsm;
	spin_lock_init(&fhsm->fhsm_spin);
	init_waitqueue_head(&fhsm->fhsm_wqh);
	atomic_set(&fhsm->fhsm_readable, 0);
	fhsm->fhsm_expire
		= msecs_to_jiffies(AUFS_FHSM_CACHE_DEF_SEC * MSEC_PER_SEC);
	fhsm->fhsm_bottom = -1;
}

void au_fhsm_set(struct au_sbinfo *sbinfo, unsigned int sec)
{
	sbinfo->si_fhsm.fhsm_expire
		= msecs_to_jiffies(sec * MSEC_PER_SEC);
}

void au_fhsm_show(struct seq_file *seq, struct au_sbinfo *sbinfo)
{
	unsigned int u;

	if (!au_ftest_si(sbinfo, FHSM))
		return;

	u = jiffies_to_msecs(sbinfo->si_fhsm.fhsm_expire) / MSEC_PER_SEC;
	if (u != AUFS_FHSM_CACHE_DEF_SEC)
		seq_printf(seq, ",fhsm_sec=%u", u);
}