// SPDX-License-Identifier: CDDL-1.0
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or https://opensource.org/licenses/CDDL-1.0.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2011, Lawrence Livermore National Security, LLC.
 * Copyright (c) 2023, Datto Inc. All rights reserved.
 * Copyright (c) 2025, Klara, Inc.
 * Copyright (c) 2025, Rob Norris <robn@despairlabs.com>
 * Copyright (c) 2026, TrueNAS.
 */


#include <sys/zfs_znode.h>
#include <sys/zfs_vfsops.h>
#include <sys/zfs_vnops.h>
#include <sys/zfs_ctldir.h>
#include <sys/zpl.h>
#include <linux/iversion.h>
#include <linux/version.h>
#include <linux/vfs_compat.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>

/*
 * What to do when the last reference to an inode is released. If 0, the kernel
 * will cache it on the superblock. If 1, the inode will be freed immediately.
 * See zpl_drop_inode().
 */
int zfs_delete_inode = 0;

/*
 * What to do when the last reference to a dentry is released. If 0, the kernel
 * will cache it until the entry (file) is destroyed. If 1, the dentry will be
 * marked for cleanup, at which time its inode reference will be released. See
 * zpl_dentry_delete().
 */
int zfs_delete_dentry = 0;

static struct inode *
zpl_inode_alloc(struct super_block *sb)
{
	struct inode *ip;

	VERIFY3S(zfs_inode_alloc(sb, &ip), ==, 0);
	inode_set_iversion(ip, 1);

	return (ip);
}

#ifdef HAVE_SOPS_FREE_INODE
static void
zpl_inode_free(struct inode *ip)
{
	ASSERT0(atomic_read(&ip->i_count));
	zfs_inode_free(ip);
}
#endif

static void
zpl_inode_destroy(struct inode *ip)
{
	ASSERT0(atomic_read(&ip->i_count));
	zfs_inode_destroy(ip);
}

/*
 * Called from __mark_inode_dirty() to reflect that something in the
 * inode has changed.  We use it to ensure the znode system attributes
 * are always strictly update to date with respect to the inode.
 */
static void
zpl_dirty_inode(struct inode *ip, int flags)
{
	fstrans_cookie_t cookie;

	cookie = spl_fstrans_mark();
	zfs_dirty_inode(ip, flags);
	spl_fstrans_unmark(cookie);
}

/*
 * ->drop_inode() is called when the last reference to an inode is released.
 * Its return value indicates if the inode should be destroyed immediately, or
 * cached on the superblock structure.
 *
 * By default (zfs_delete_inode=0), we call generic_drop_inode(), which returns
 * "destroy immediately" if the inode is unhashed and has no links (roughly: no
 * longer exists on disk). On datasets with millions of rarely-accessed files,
 * this can cause a large amount of memory to be "pinned" by cached inodes,
 * which in turn pin their associated dnodes and dbufs, until the kernel starts
 * reporting memory pressure and requests OpenZFS release some memory (see
 * zfs_prune()).
 *
 * When set to 1, we call generic_delete_inode(), which always returns "destroy
 * immediately", resulting in inodes being destroyed immediately, releasing
 * their associated dnodes and dbufs to the dbuf cached and the ARC to be
 * evicted as normal.
 *
 * Note that the "last reference" doesn't always mean the last _userspace_
 * reference; the dentry cache also holds a reference, so "busy" inodes will
 * still be kept alive that way (subject to dcache tuning).
 */
static int
zpl_drop_inode(struct inode *ip)
{
	if (zfs_delete_inode)
		return (generic_delete_inode(ip));
	return (generic_drop_inode(ip));
}

/*
 * The ->evict_inode() callback must minimally truncate the inode pages,
 * and call clear_inode().  For 2.6.35 and later kernels this will
 * simply update the inode state, with the sync occurring before the
 * truncate in evict().  For earlier kernels clear_inode() maps to
 * end_writeback() which is responsible for completing all outstanding
 * write back.  In either case, once this is done it is safe to cleanup
 * any remaining inode specific data via zfs_inactive().
 * remaining filesystem specific data.
 */
static void
zpl_evict_inode(struct inode *ip)
{
	fstrans_cookie_t cookie;

	cookie = spl_fstrans_mark();
	truncate_setsize(ip, 0);
	clear_inode(ip);
	zfs_inactive(ip);
	spl_fstrans_unmark(cookie);
}

static void
zpl_put_super(struct super_block *sb)
{
	fstrans_cookie_t cookie;
	int error;

	cookie = spl_fstrans_mark();
	error = -zfs_umount(sb);
	spl_fstrans_unmark(cookie);
	ASSERT3S(error, <=, 0);
}

/*
 * zfs_sync() is the underlying implementation for the sync(2) and syncfs(2)
 * syscalls, via sb->s_op->sync_fs().
 *
 * Before kernel 5.17 (torvalds/linux@5679897eb104), syncfs() ->
 * sync_filesystem() would ignore the return from sync_fs(), instead only
 * considing the error from syncing the underlying block device (sb->s_dev).
 * Since OpenZFS doesn't _have_ an underlying block device, there's no way for
 * us to report a sync directly.
 *
 * However, in 5.8 (torvalds/linux@735e4ae5ba28) the superblock gained an extra
 * error store `s_wb_err`, to carry errors seen on page writeback since the
 * last call to syncfs(). If sync_filesystem() does not return an error, any
 * existing writeback error on the superblock will be used instead (and cleared
 * either way). We don't use this (page writeback is a different thing for us),
 * so for 5.8-5.17 we can use that instead to get syncfs() to return the error.
 *
 * Before 5.8, we have no other good options - no matter what happens, the
 * userspace program will be told the call has succeeded, and so we must make
 * it so, Therefore, when we are asked to wait for sync to complete (wait ==
 * 1), if zfs_sync() has returned an error we have no choice but to block,
 * regardless of the reason.
 *
 * The 5.17 change was backported to the 5.10, 5.15 and 5.16 series, and likely
 * to some vendor kernels. Meanwhile, s_wb_err is still in use in 6.15 (the
 * mainline Linux series at time of writing), and has likely been backported to
 * vendor kernels before 5.8. We don't really want to use a workaround when we
 * don't have to, but we can't really detect whether or not sync_filesystem()
 * will return our errors (without a difficult runtime test anyway). So, we use
 * a static version check: any kernel reporting its version as 5.17+ will use a
 * direct error return, otherwise, we'll either use s_wb_err if it was detected
 * at configure (5.8-5.16 + vendor backports). If it's unavailable, we will
 * block to ensure the correct semantics.
 *
 * See https://github.com/openzfs/zfs/issues/17416 for further discussion.
 */
static int
zpl_sync_fs(struct super_block *sb, int wait)
{
	fstrans_cookie_t cookie;
	cred_t *cr = CRED();
	int error;

	crhold(cr);
	cookie = spl_fstrans_mark();
	error = -zfs_sync(sb, wait, cr);

#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 17, 0)
#ifdef HAVE_SUPER_BLOCK_S_WB_ERR
	if (error && wait)
		errseq_set(&sb->s_wb_err, error);
#else
	if (error && wait) {
		zfsvfs_t *zfsvfs = sb->s_fs_info;
		ASSERT3P(zfsvfs, !=, NULL);
		if (zfs_enter(zfsvfs, FTAG) == 0) {
			txg_wait_synced(dmu_objset_pool(zfsvfs->z_os), 0);
			zfs_exit(zfsvfs, FTAG);
			error = 0;
		}
	}
#endif
#endif /* < 5.17.0 */

	spl_fstrans_unmark(cookie);
	crfree(cr);

	ASSERT3S(error, <=, 0);
	return (error);
}

static int
zpl_statfs(struct dentry *dentry, struct kstatfs *statp)
{
	fstrans_cookie_t cookie;
	int error;

	cookie = spl_fstrans_mark();
	error = -zfs_statvfs(dentry->d_inode, statp);
	spl_fstrans_unmark(cookie);
	ASSERT3S(error, <=, 0);

	/*
	 * If required by a 32-bit system call, dynamically scale the
	 * block size up to 16MiB and decrease the block counts.  This
	 * allows for a maximum size of 64EiB to be reported.  The file
	 * counts must be artificially capped at 2^32-1.
	 */
	if (unlikely(zpl_is_32bit_api())) {
		while (statp->f_blocks > UINT32_MAX &&
		    statp->f_bsize < SPA_MAXBLOCKSIZE) {
			statp->f_frsize <<= 1;
			statp->f_bsize <<= 1;

			statp->f_blocks >>= 1;
			statp->f_bfree >>= 1;
			statp->f_bavail >>= 1;
		}

		uint64_t usedobjs = statp->f_files - statp->f_ffree;
		statp->f_ffree = MIN(statp->f_ffree, UINT32_MAX - usedobjs);
		statp->f_files = statp->f_ffree + usedobjs;
	}

	return (error);
}

static int
__zpl_show_devname(struct seq_file *seq, zfsvfs_t *zfsvfs)
{
	int error;
	if ((error = zpl_enter(zfsvfs, FTAG)) != 0)
		return (error);

	char *fsname = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP);
	dmu_objset_name(zfsvfs->z_os, fsname);

	for (int i = 0; fsname[i] != 0; i++) {
		/*
		 * Spaces in the dataset name must be converted to their
		 * octal escape sequence for getmntent(3) to correctly
		 * parse then fsname portion of /proc/self/mounts.
		 */
		if (fsname[i] == ' ') {
			seq_puts(seq, "\\040");
		} else {
			seq_putc(seq, fsname[i]);
		}
	}

	kmem_free(fsname, ZFS_MAX_DATASET_NAME_LEN);

	zpl_exit(zfsvfs, FTAG);

	return (0);
}

static int
zpl_show_devname(struct seq_file *seq, struct dentry *root)
{
	return (__zpl_show_devname(seq, root->d_sb->s_fs_info));
}

static int
__zpl_show_options(struct seq_file *seq, zfsvfs_t *zfsvfs)
{
	seq_printf(seq, ",%s",
	    zfsvfs->z_flags & ZSB_XATTR ? "xattr" : "noxattr");

#ifdef CONFIG_FS_POSIX_ACL
	switch (zfsvfs->z_acl_type) {
	case ZFS_ACLTYPE_POSIX:
		seq_puts(seq, ",posixacl");
		break;
	default:
		seq_puts(seq, ",noacl");
		break;
	}
#endif /* CONFIG_FS_POSIX_ACL */

	switch (zfsvfs->z_case) {
	case ZFS_CASE_SENSITIVE:
		seq_puts(seq, ",casesensitive");
		break;
	case ZFS_CASE_INSENSITIVE:
		seq_puts(seq, ",caseinsensitive");
		break;
	default:
		seq_puts(seq, ",casemixed");
		break;
	}

	return (0);
}

static int
zpl_show_options(struct seq_file *seq, struct dentry *root)
{
	return (__zpl_show_options(seq, root->d_sb->s_fs_info));
}

static int
zpl_test_super(struct super_block *s, void *data)
{
	zfsvfs_t *zfsvfs = s->s_fs_info;
	objset_t *os = data;
	/*
	 * If the os doesn't match the z_os in the super_block, assume it is
	 * not a match. Matching would imply a multimount of a dataset. It is
	 * possible that during a multimount, there is a simultaneous operation
	 * that changes the z_os, e.g., rollback, where the match will be
	 * missed, but in that case the user will get an EBUSY.
	 */
	return (zfsvfs != NULL && os == zfsvfs->z_os);
}

static void
zpl_kill_sb(struct super_block *sb)
{
	zfs_preumount(sb);
	kill_anon_super(sb);
}

void
zpl_prune_sb(uint64_t nr_to_scan, void *arg)
{
	struct super_block *sb = (struct super_block *)arg;
	int objects = 0;

	/*
	 * Ensure the superblock is not in the process of being torn down.
	 */
#ifdef HAVE_SB_DYING
	if (down_read_trylock(&sb->s_umount)) {
		if (!(sb->s_flags & SB_DYING) && sb->s_root &&
		    (sb->s_flags & SB_BORN)) {
			(void) zfs_prune(sb, nr_to_scan, &objects);
		}
		up_read(&sb->s_umount);
	}
#else
	if (down_read_trylock(&sb->s_umount)) {
		if (!hlist_unhashed(&sb->s_instances) &&
		    sb->s_root && (sb->s_flags & SB_BORN)) {
			(void) zfs_prune(sb, nr_to_scan, &objects);
		}
		up_read(&sb->s_umount);
	}
#endif
}

/*
 * Mount option parsing.
 *
 * The kernel receives a set of "stringy" mount options, typically a
 * comma-separated list through mount(2) or fsconfig(2). These are split into a
 * set of struct fs_parameter, and then vfs_parse_fs_param() is called for
 * each. That function will handle (and consume) some options directly, and
 * other subsystems (mainly security modules) are given the opportunity to
 * consume them too. Any left over are passed to zpl_parse_param(). Our job is
 * to use them to fill in the vfs_t we've attached previously to
 * fc->fs_private, ready for the mount or remount call when it comes.
 *
 * Historically, mount options have been generated, removed, modified and
 * otherwise complicated by multiple different actors over a long time: the
 * kernel itself, the original mount(8) utility and later libmount,
 * mount.zfs(8), libzfs and the ZFS tools that use it, and any program using
 * the various mount APIs that have come and gone over the years. This is
 * further complicated by cross-pollination between OpenSolaris/illumos, Linux
 * and FreeBSD. Long story short: we could see all sorts of things, and we need
 * to at least try not to break old userspace programs.
 *
 * At time of writing, this is my best understanding of all the options we
 * might reasonably see, and where and how they're handled.
 *
 *
 * These are common options for all filesystems that are processed by the
 * kernel directly, without zpl_parse_param() being called. They're a bit of a
 * mixed bag, but are ultimately all available to us via either sb->s_flags or
 * fc->sb_flags:
 *
 *	dirsync:	set SB_DIRSYNC
 *	lazytime:	set SB_LAZYTIME
 *	mand:		set SB_MANDLOCK
 *	ro:		set SB_RDONLY
 *	sync:		set SB_SYNCHRONOUS
 *
 *	async:		clear SB_SYNCHRONOUS
 *	nolazytime:	clear SB_LAZYTIME
 *	nomand:		clear SB_MANDLOCK
 *	rw:		clear SB_RDONLY
 *
 * Fortunately, almost all of these are handled directly by the kernel. 'mand'
 * and 'nomand' are swallowed by the kernel ('mand' emits a warning in the
 * kernel log), but it and the corresponding dataset property have been a no-op
 * in OpenZFS for years, so there's nothing for us to do there.
 *
 * The only tricky one is SB_RDONLY ('ro'/'rw'), which can be both a mount and
 * a superblock option. While we won't receive the "stringy" options, the
 * kernel will set it for us in fc->sb_flags, and we've always had special
 * handling for it at mount and remount time (eg handling snapshot mounts), so
 * it's not a problem to do nothing here because we will sort it out later.
 *
 *
 * These are options that we may receive as "stringy" options but also as mount
 * flags.
 *
 *	exec:		clear MS_NOEXEC
 *	noexec:		set MS_NOEXEC
 *	suid:		clear MS_NOSUID
 *	nosuid:		set MS_NOSUID
 *	dev:		clear MS_NODEV
 *	nodev:		set MS_NODEV
 *	atime:		clear MS_NOATIME
 *	noatime:	set MS_NOATIME
 *	relatime:	set MS_RELATIME
 *	norelatime:	clear MS_RELATIME
 *
 * In testing, it appears that recent libmount will convert them, but our own
 * mount code (libzfs_mount) may not. We will be called for the stringy
 * versions, but not for the flags. The flags will later be available on
 * vfsmount->mnt_flags, not set on the vfs_t. This tends not to matter in
 * practice, as almost all mounts come through libzfs (via zfs-mount(8) or
 * mount.zfs(8)) and so as strings, and when they do come through flags, they
 * will still be reported correctly via mountinfo and by zfs-get(8), which has
 * special handling for "temporary" properties. Also, we never use these
 * internally for any decisions; 'exec', 'suid' and 'dev' are handled in the
 * kernel, and the kernel provides helpers for 'atime' and 'relatime'. The
 * only place the difference is observable is through zfs_get_temporary_prop(),
 * which is only used by the zfs.get_prop() Lua call.
 *
 * This is fixable by getting at vfsmount->mnt_flags, but this is not readily
 * available until after the mount operation is completed, and with some
 * effort. This is all very low impact, so it's left for future improvement.
 *
 *
 * These are true OpenZFS-specific mount options. They give the equivalent
 * of temporarily setting the pool properties as follows:
 *
 *	strictatime	atime=on, relatime=off
 *
 *	xattr:		xattr=sa
 *	saxattr:	xattr=sa
 *	dirxattr:	xattr=dir
 *	noxattr:	xattr=off
 *
 *
 * mntpoint= provides the canonical mount point for a snapshot mount. This
 * is an assist for the snapshot automounter call out to userspace, to
 * understand where the snapshot is mounted even when triggered from an
 * alternate mount namespace (eg inside a chroot).
 *
 *	mntpoint=	vfs->vfs_mntpoint=...
 *
 *
 * These are used for coordination inside libzfs, and should not make it
 * to the kernel, but it does not strip them, so we handle them and ignore
 * them.
 *
 *	defaults
 *	zfsutil
 *	remount
 *
 *
 * These are specific to SELinux. When that security module is running, it
 * will consume them, but if not, they will be passed through to us. libzfs
 * adds them unconditionally, so we will always see them when SELinux is not
 * running, and ignore them.
 *
 *	fscontext
 *	defcontext
 *	rootcontext
 *	context
 *
 *
 * When preparing a remount, libmount will read /proc/self/mountinfo and add
 * any unrecognised flags it finds there to the options. So, we have to accept
 * anything that __zpl_show_options() can produce.
 *
 *	posixacl
 *	noacl
 *	casesensitive
 *	caseinsensitive
 *	casemixed
 *
 *
 * mount(8) has a notion of "sloppy" options. According to the documentation,
 * when the -s switch is provided, unrecognised mount options will be ignored.
 * Only the Linux NFS and SMB filesystems support it, and traditionally
 * OpenZFS has too. however, it appears massively underspecified and
 * inconsistent. Depending on the interplay between mount(8), the mount helper
 * (eg mount.zfs(8)) and libmount, -s may cause unknown options to be filtered
 * in userspace, _or_ an additional option 'sloppy' to be passed to the kernel
 * either before or after the "unknown" option, _or_ nothing at all happens
 * and the unknown option to be passed through to the kernel as-is. The
 * kernel NFS and SMB filesystems both expect to see an explicit option
 * 'sloppy' and use this to either ignore or reject unknown options, but as
 * described, it's very easy for that option to not appear, or appear too late.
 *
 * OpenZFS has a test for this in the test suite, and it's documented in
 * mount.zfs(8), so to support it we accept 'sloppy' and ignore it, and all
 * other unknown options produce a notice in the kernel log, and are also
 * ignored. This allows the "feature" to continue to work, while avoiding
 * the additional housekeeping for the 'sloppy' option.
 *
 *	sloppy
 *
 *
 * Finally, all filesystems get automatic handling for the 'source' option,
 * that is, the "name" of the filesystem (the first column of df(1)'s output).
 * However, this only happens if the handler does not otherwise handle
 * the 'source' option. Since we handle _all_ options because of 'sloppy', we
 * deal with this explicitly by calling into the kernel's helper for this,
 * vfs_parse_fs_param_source(), which sets up fc->source.
 *
 *	source
 *
 *
 * Thank you for reading this far. I hope you find what you are looking for,
 * in this life or the next.
 *
 *   -- robn, 2026-03-26
 */

enum {
	Opt_exec, Opt_suid, Opt_dev,
	Opt_atime, Opt_relatime, Opt_strictatime,
	Opt_saxattr, Opt_dirxattr, Opt_noxattr,
	Opt_mntpoint,

	Opt_ignore, Opt_warn,
};

static const struct fs_parameter_spec zpl_param_spec[] = {
	fsparam_flag_no("exec",		Opt_exec),
	fsparam_flag_no("suid",		Opt_suid),
	fsparam_flag_no("dev",		Opt_dev),

	fsparam_flag_no("atime",	Opt_atime),
	fsparam_flag_no("relatime",	Opt_relatime),
	fsparam_flag("strictatime",	Opt_strictatime),

	fsparam_flag("xattr",		Opt_saxattr),
	fsparam_flag("saxattr",		Opt_saxattr),
	fsparam_flag("dirxattr",	Opt_dirxattr),
	fsparam_flag("noxattr",		Opt_noxattr),

	fsparam_string("mntpoint",	Opt_mntpoint),

	fsparam_flag("defaults",	Opt_ignore),
	fsparam_flag("zfsutil",		Opt_ignore),
	fsparam_flag("remount",		Opt_ignore),

	fsparam_string("fscontext",	Opt_ignore),
	fsparam_string("defcontext",	Opt_ignore),
	fsparam_string("rootcontext",	Opt_ignore),
	fsparam_string("context",	Opt_ignore),

	fsparam_flag("posixacl",	Opt_ignore),
	fsparam_flag("noacl",		Opt_ignore),
	fsparam_flag("casesensitive",	Opt_ignore),
	fsparam_flag("caseinsensitive",	Opt_ignore),
	fsparam_flag("casemixed",	Opt_ignore),

	fsparam_flag("sloppy",		Opt_ignore),

	{}
};

static int
zpl_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
	vfs_t *vfs = fc->fs_private;

	/* Handle 'source' explicitly so we don't trip on it as an unknown. */
	int opt = vfs_parse_fs_param_source(fc, param);
	if (opt != -ENOPARAM)
		return (opt);

	struct fs_parse_result result;
	opt = fs_parse(fc, zpl_param_spec, param, &result);
	if (opt == -ENOPARAM) {
		/*
		 * Convert unknowns to warnings, to work around the whole
		 * "sloppy option" mess.
		 */
		opt = Opt_warn;
	}
	if (opt < 0)
		return (opt);

	switch (opt) {
	case Opt_exec:
		vfs->vfs_exec = !result.negated;
		vfs->vfs_do_exec = B_TRUE;
		break;
	case Opt_suid:
		vfs->vfs_setuid = !result.negated;
		vfs->vfs_do_setuid = B_TRUE;
		break;
	case Opt_dev:
		vfs->vfs_devices = !result.negated;
		vfs->vfs_do_devices = B_TRUE;
		break;

	case Opt_atime:
		vfs->vfs_atime = !result.negated;
		vfs->vfs_do_atime = B_TRUE;
		break;
	case Opt_relatime:
		vfs->vfs_relatime = !result.negated;
		vfs->vfs_do_relatime = B_TRUE;
		break;
	case Opt_strictatime:
		vfs->vfs_atime = B_TRUE;
		vfs->vfs_do_atime = B_TRUE;
		vfs->vfs_relatime = B_FALSE;
		vfs->vfs_do_relatime = B_TRUE;
		break;

	case Opt_saxattr:
		vfs->vfs_xattr = ZFS_XATTR_SA;
		vfs->vfs_do_xattr = B_TRUE;
		break;
	case Opt_dirxattr:
		vfs->vfs_xattr = ZFS_XATTR_DIR;
		vfs->vfs_do_xattr = B_TRUE;
		break;
	case Opt_noxattr:
		vfs->vfs_xattr = ZFS_XATTR_OFF;
		vfs->vfs_do_xattr = B_TRUE;
		break;

	case Opt_mntpoint:
		if (vfs->vfs_mntpoint != NULL)
			kmem_strfree(vfs->vfs_mntpoint);
		vfs->vfs_mntpoint = kmem_strdup(param->string);
		break;

	case Opt_ignore:
		break;

	case Opt_warn:
		cmn_err(CE_NOTE,
		    "ZFS: ignoring unknown mount option: %s", param->key);
		break;

	default:
		return (-SET_ERROR(EINVAL));
	}

	return (0);
}

/*
 * Before Linux 5.8, the kernel's individual parameter parsing had a list of
 * "forbidden" options that would always be rejected early. These were options
 * that should be specified by MS_* flags, to be set on the superblock
 * directly. However, it was inconsistently applied (eg it had various "*atime"
 * options but not "atime", and also caused problems when it was not in sync
 * with the version of libmount in use. It was deemed needlessly restrictive
 * and was dropped in torvalds/linux@9193ae87a8af.
 *
 * Unfortunately, some of the options on this list are used by OpenZFS, so
 * we need to see them. These include the aforementioned "*atime", "dev",
 * "exec" and "suid".
 *
 * There is no easy compile-time check available to detect this, so we use
 * a simple version check that should make it available everywhere needed,
 * most notably RHEL8's 4.18+extras, which has backported fs_context support
 * but does not include the 5.8 commit.
 */
#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
#define	HAVE_FORBIDDEN_SB_FLAGS	1
#endif

#ifdef HAVE_FORBIDDEN_SB_FLAGS
/*
 * The typical path for options parsing through mount(2) is:
 *
 *     ksys_mount
 *     do_mount
 *     generic_parse_monolithic
 *     vfs_parse_fs_string
 *     vfs_parse_fs_param
 *     zpl_parse_param
 *
 * vfs_parse_fs_param() calls the internal vfs_parse_sb_flag(), which is
 * where the "forbidden" flags are applied. If it makes it through there,
 * it will later call fc->parse_param() ie zpl_parse_param(). We can't
 * intercept this chain in the middle anywhere; the earliest thing we can
 * override is generic_parse_monolithic(), substituting our own by setting
 * fc->parse_monolithic and doing the parsing work ourselves.
 *
 * Fortunately, generic_parse_monolithic() is almost entirely splitting the
 * incoming parameter string on comma and handing off to the rest of the
 * pipeline. This is easily replaced (almost entirely by reviving a few bits
 * of our old options parser).
 *
 * To keep the change as narrow as possible, we reuse zpl_param_spec and
 * zpl_parse_param() as much as possible. Once we've parsed the option, we call
 * fs_parse(zpl_param_spec) to find out if the option is actually one we
 * explicitly care about. If it is, we call zpl_parse_param() directly,
 * avoiding vfs_parse_fs_param() and so the risk of being rejected. If it is
 * not one we explicitly care about, we call zpl_parse_param() as normal,
 * letting the kernel reject it if it wishes. If it doesn't, it will end up
 * back in zpl_parse_param() via fc->parse_param, and we can ignore or warn
 * about it we normally would.
 */
static int
zpl_parse_monolithic(struct fs_context *fc, void *data)
{
	char *mntopts = data;

	if (mntopts == NULL)
		return (0);

	/*
	 * Because we supply a .parse_monolithic callback, the kernel does
	 * no consideration of the options blob at all. Because of this, we
	 * have to give LSMs a first look at it. They will remove any options
	 * of interest to them (eg the SELinux *context= options).
	 */
	int err = security_sb_eat_lsm_opts(mntopts, &fc->security);
	if (err)
		return (err);

	char *key;
	while ((key = strsep(&mntopts, ",")) != NULL) {
		if (!*key)
			continue;

		struct fs_parameter param = {
		    .key = key,
		};

		char *value = strchr(key, '=');
		if (value != NULL) {
			/* Key starts with '='. Kernel ignores, we will too. */
			if (value == key)
				continue;
			*value++ = '\0';

			/* key=value is a "string" type, set up for that */
			param.string = value;
			param.type = fs_value_is_string;
			param.size = strlen(value);
		} else {
			/* unadorned key is a "flag" type */
			param.type = fs_value_is_flag;
		}

		/* Check if this is one of our options. */
		struct fs_parse_result result;
		int opt = fs_parse(fc, zpl_param_spec, &param, &result);
		if (opt >= 0) {
			/*
			 * We already know this one of our options, so a
			 * failure here would be nonsensical.
			 */
			VERIFY0(zpl_parse_param(fc, &param));
		} else {
			/*
			 * Not one of our option, send it through the kernel's
			 * standard parameter handling.
			 */
			err = vfs_parse_fs_param(fc, &param);
			if (err < 0)
				return (err);
		}
	}

	return (0);
}
#endif /* HAVE_FORBIDDEN_SB_FLAGS */

static int
zpl_get_tree(struct fs_context *fc)
{
	struct super_block *sb;
	objset_t *os;
	boolean_t issnap = B_FALSE;
	int err;

	err = dmu_objset_hold(fc->source, FTAG, &os);
	if (err)
		return (-err);

	/*
	 * The dsl pool lock must be released prior to calling sget().
	 * It is possible sget() may block on the lock in grab_super()
	 * while deactivate_super() holds that same lock and waits for
	 * a txg sync.  If the dsl_pool lock is held over sget()
	 * this can prevent the pool sync and cause a deadlock.
	 */
	dsl_dataset_long_hold(dmu_objset_ds(os), FTAG);
	dsl_pool_rele(dmu_objset_pool(os), FTAG);

	sb = sget(fc->fs_type, zpl_test_super, set_anon_super,
	    fc->sb_flags, os);

	/*
	 * Recheck with the lock held to prevent mounting the wrong dataset
	 * since z_os can be stale when the teardown lock is held.
	 *
	 * We can't do this in zpl_test_super in since it's under spinlock and
	 * also s_umount lock is not held there so it would race with
	 * zfs_umount and zfsvfs can be freed.
	 */
	if (!IS_ERR(sb) && sb->s_fs_info != NULL) {
		zfsvfs_t *zfsvfs = sb->s_fs_info;
		if (zpl_enter(zfsvfs, FTAG) == 0) {
			if (os != zfsvfs->z_os)
				err = SET_ERROR(EBUSY);
			issnap = zfsvfs->z_issnap;
			zpl_exit(zfsvfs, FTAG);
		} else {
			err = SET_ERROR(EBUSY);
		}
	}
	dsl_dataset_long_rele(dmu_objset_ds(os), FTAG);
	dsl_dataset_rele(dmu_objset_ds(os), FTAG);

	if (IS_ERR(sb))
		return (PTR_ERR(sb));

	if (err) {
		deactivate_locked_super(sb);
		return (-err);
	}

	if (sb->s_root == NULL) {
		vfs_t *vfs = fc->fs_private;

		/* Apply readonly flag as mount option */
		if (fc->sb_flags & SB_RDONLY) {
			vfs->vfs_readonly = B_TRUE;
			vfs->vfs_do_readonly = B_TRUE;
		}

		fstrans_cookie_t cookie = spl_fstrans_mark();
		err = zfs_domount(sb, fc->source, vfs,
		    fc->sb_flags & SB_SILENT ? 1 : 0);
		spl_fstrans_unmark(cookie);

		if (err) {
			deactivate_locked_super(sb);
			return (-err);
		}

		/*
		 * zfsvfs has taken ownership of the mount options, so we
		 * need to ensure we don't free them.
		 */
		fc->fs_private = NULL;

		sb->s_flags |= SB_ACTIVE;
	} else if (!issnap && ((fc->sb_flags ^ sb->s_flags) & SB_RDONLY)) {
		/*
		 * Skip ro check for snap since snap is always ro regardless
		 * ro flag is passed by mount or not.
		 */
		deactivate_locked_super(sb);
		return (-SET_ERROR(EBUSY));
	}

	struct dentry *root = dget(sb->s_root);
	if (IS_ERR(root))
		return (PTR_ERR(root));

	fc->root = root;
	return (0);
}

static int
zpl_reconfigure(struct fs_context *fc)
{
	fstrans_cookie_t cookie;
	int error;

	cookie = spl_fstrans_mark();
	error = -zfs_remount(fc->root->d_sb, fc->fs_private, fc->sb_flags);
	spl_fstrans_unmark(cookie);
	ASSERT3S(error, <=, 0);

	if (error == 0) {
		/*
		 * zfsvfs has taken ownership of the mount options, so we
		 * need to ensure we don't free them.
		 */
		fc->fs_private = NULL;
	}

	return (error);
}

static int
zpl_dup_fc(struct fs_context *fc, struct fs_context *src_fc)
{
	vfs_t *src_vfs = src_fc->fs_private;
	if (src_vfs == NULL)
		return (0);

	vfs_t *vfs = zfsvfs_vfs_alloc();
	if (vfs == NULL)
		return (-SET_ERROR(ENOMEM));

	/*
	 * This is annoying, but a straight memcpy() would require us to
	 * reinitialise the lock.
	 */
	vfs->vfs_xattr = src_vfs->vfs_xattr;
	vfs->vfs_readonly = src_vfs->vfs_readonly;
	vfs->vfs_do_readonly = src_vfs->vfs_do_readonly;
	vfs->vfs_setuid = src_vfs->vfs_setuid;
	vfs->vfs_do_setuid = src_vfs->vfs_do_setuid;
	vfs->vfs_exec = src_vfs->vfs_exec;
	vfs->vfs_do_exec = src_vfs->vfs_do_exec;
	vfs->vfs_devices = src_vfs->vfs_devices;
	vfs->vfs_do_devices = src_vfs->vfs_do_devices;
	vfs->vfs_do_xattr = src_vfs->vfs_do_xattr;
	vfs->vfs_atime = src_vfs->vfs_atime;
	vfs->vfs_do_atime = src_vfs->vfs_do_atime;
	vfs->vfs_relatime = src_vfs->vfs_relatime;
	vfs->vfs_do_relatime = src_vfs->vfs_do_relatime;
	vfs->vfs_nbmand = src_vfs->vfs_nbmand;
	vfs->vfs_do_nbmand = src_vfs->vfs_do_nbmand;

	mutex_enter(&src_vfs->vfs_mntpt_lock);
	if (src_vfs->vfs_mntpoint != NULL)
		vfs->vfs_mntpoint = kmem_strdup(src_vfs->vfs_mntpoint);
	mutex_exit(&src_vfs->vfs_mntpt_lock);

	fc->fs_private = vfs;
	return (0);
}

static void
zpl_free_fc(struct fs_context *fc)
{
	zfsvfs_vfs_free(fc->fs_private);
}

const struct fs_context_operations zpl_fs_context_operations = {
#ifdef	HAVE_FORBIDDEN_SB_FLAGS
	.parse_monolithic	= zpl_parse_monolithic,
#endif
	.parse_param		= zpl_parse_param,
	.get_tree		= zpl_get_tree,
	.reconfigure		= zpl_reconfigure,
	.dup			= zpl_dup_fc,
	.free			= zpl_free_fc,
};

static int
zpl_init_fs_context(struct fs_context *fc)
{
	fc->fs_private = zfsvfs_vfs_alloc();
	if (fc->fs_private == NULL)
		return (-SET_ERROR(ENOMEM));

	fc->ops = &zpl_fs_context_operations;

	return (0);
}

const struct super_operations zpl_super_operations = {
	.alloc_inode		= zpl_inode_alloc,
#ifdef HAVE_SOPS_FREE_INODE
	.free_inode		= zpl_inode_free,
#endif
	.destroy_inode		= zpl_inode_destroy,
	.dirty_inode		= zpl_dirty_inode,
	.write_inode		= NULL,
	.drop_inode		= zpl_drop_inode,
	.evict_inode		= zpl_evict_inode,
	.put_super		= zpl_put_super,
	.sync_fs		= zpl_sync_fs,
	.statfs			= zpl_statfs,
	.show_devname		= zpl_show_devname,
	.show_options		= zpl_show_options,
	.show_stats		= NULL,
};

/*
 * ->d_delete() is called when the last reference to a dentry is released. Its
 *  return value indicates if the dentry should be destroyed immediately, or
 *  retained in the dentry cache.
 *
 * By default (zfs_delete_dentry=0) the kernel will always cache unused
 * entries.  Each dentry holds an inode reference, so cached dentries can hold
 * the final inode reference indefinitely, leading to the inode and its related
 * data being pinned (see zpl_drop_inode()).
 *
 * When set to 1, we signal that the dentry should be destroyed immediately and
 * never cached. This reduces memory usage, at the cost of higher overheads to
 * lookup a file, as the inode and its underlying data (dnode/dbuf) need to be
 * reloaded and reinflated.
 *
 * Note that userspace does not have direct control over dentry references and
 * reclaim; rather, this is part of the kernel's caching and reclaim subsystems
 * (eg vm.vfs_cache_pressure).
 */
static int
zpl_dentry_delete(const struct dentry *dentry)
{
	return (zfs_delete_dentry ? 1 : 0);
}

const struct dentry_operations zpl_dentry_operations = {
	.d_delete = zpl_dentry_delete,
};

struct file_system_type zpl_fs_type = {
	.owner			= THIS_MODULE,
	.name			= ZFS_DRIVER,
#if defined(HAVE_IDMAP_MNT_API)
	.fs_flags		= FS_USERNS_MOUNT | FS_ALLOW_IDMAP,
#else
	.fs_flags		= FS_USERNS_MOUNT,
#endif
	.init_fs_context	= zpl_init_fs_context,
	.kill_sb		= zpl_kill_sb,
};

ZFS_MODULE_PARAM(zfs, zfs_, delete_inode, INT, ZMOD_RW,
	"Delete inodes as soon as the last reference is released.");

ZFS_MODULE_PARAM(zfs, zfs_, delete_dentry, INT, ZMOD_RW,
	"Delete dentries from dentry cache as soon as the last reference is "
	"released.");