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mount: use the mount syscall directly
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Allow zfs datasets to be mounted on Linux without relying on the
invocation of an external processes.  This is the same behavior
which is implemented for FreeBSD.

Use of the libmount library was originally considered because it 
provides functionality to properly lock and update the /etc/mtab 
file.  However, these days /etc/mtab is typically a symlink to 
/proc/self/mounts so there's nothing to updated.  Therefore, we
call mount(2) directly and avoid any additional dependencies. 

If required the legacy behavior can be enabled by setting the 
ZFS_MOUNT_HELPER environment variable.  This may be needed in
environments where SELinux in enabled and the zfs binary does  
not have mount permission.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Felix Dörre <felix@dogcraft.de>
#10294
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@felixdoerre
felixdoerre authored May 21, 2020
1 parent 57434ab commit 501a151
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Showing 9 changed files with 335 additions and 277 deletions.
236 changes: 2 additions & 234 deletions cmd/mount_zfs/mount_zfs.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,185 +42,6 @@

libzfs_handle_t *g_zfs;

typedef struct option_map {
const char *name;
unsigned long mntmask;
unsigned long zfsmask;
} option_map_t;

static const option_map_t option_map[] = {
/* Canonicalized filesystem independent options from mount(8) */
{ MNTOPT_NOAUTO, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_DEFAULTS, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_NODEVICES, MS_NODEV, ZS_COMMENT },
{ MNTOPT_DIRSYNC, MS_DIRSYNC, ZS_COMMENT },
{ MNTOPT_NOEXEC, MS_NOEXEC, ZS_COMMENT },
{ MNTOPT_GROUP, MS_GROUP, ZS_COMMENT },
{ MNTOPT_NETDEV, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_NOFAIL, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_NOSUID, MS_NOSUID, ZS_COMMENT },
{ MNTOPT_OWNER, MS_OWNER, ZS_COMMENT },
{ MNTOPT_REMOUNT, MS_REMOUNT, ZS_COMMENT },
{ MNTOPT_RO, MS_RDONLY, ZS_COMMENT },
{ MNTOPT_RW, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_SYNC, MS_SYNCHRONOUS, ZS_COMMENT },
{ MNTOPT_USER, MS_USERS, ZS_COMMENT },
{ MNTOPT_USERS, MS_USERS, ZS_COMMENT },
/* acl flags passed with util-linux-2.24 mount command */
{ MNTOPT_ACL, MS_POSIXACL, ZS_COMMENT },
{ MNTOPT_NOACL, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_POSIXACL, MS_POSIXACL, ZS_COMMENT },
#ifdef MS_NOATIME
{ MNTOPT_NOATIME, MS_NOATIME, ZS_COMMENT },
#endif
#ifdef MS_NODIRATIME
{ MNTOPT_NODIRATIME, MS_NODIRATIME, ZS_COMMENT },
#endif
#ifdef MS_RELATIME
{ MNTOPT_RELATIME, MS_RELATIME, ZS_COMMENT },
#endif
#ifdef MS_STRICTATIME
{ MNTOPT_STRICTATIME, MS_STRICTATIME, ZS_COMMENT },
#endif
#ifdef MS_LAZYTIME
{ MNTOPT_LAZYTIME, MS_LAZYTIME, ZS_COMMENT },
#endif
{ MNTOPT_CONTEXT, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_FSCONTEXT, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_DEFCONTEXT, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_ROOTCONTEXT, MS_COMMENT, ZS_COMMENT },
#ifdef MS_I_VERSION
{ MNTOPT_IVERSION, MS_I_VERSION, ZS_COMMENT },
#endif
#ifdef MS_MANDLOCK
{ MNTOPT_NBMAND, MS_MANDLOCK, ZS_COMMENT },
#endif
/* Valid options not found in mount(8) */
{ MNTOPT_BIND, MS_BIND, ZS_COMMENT },
#ifdef MS_REC
{ MNTOPT_RBIND, MS_BIND|MS_REC, ZS_COMMENT },
#endif
{ MNTOPT_COMMENT, MS_COMMENT, ZS_COMMENT },
#ifdef MS_NOSUB
{ MNTOPT_NOSUB, MS_NOSUB, ZS_COMMENT },
#endif
#ifdef MS_SILENT
{ MNTOPT_QUIET, MS_SILENT, ZS_COMMENT },
#endif
/* Custom zfs options */
{ MNTOPT_XATTR, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_NOXATTR, MS_COMMENT, ZS_COMMENT },
{ MNTOPT_ZFSUTIL, MS_COMMENT, ZS_ZFSUTIL },
{ NULL, 0, 0 } };

/*
* Break the mount option in to a name/value pair. The name is
* validated against the option map and mount flags set accordingly.
*/
static int
parse_option(char *mntopt, unsigned long *mntflags,
unsigned long *zfsflags, int sloppy)
{
const option_map_t *opt;
char *ptr, *name, *value = NULL;
int error = 0;

name = strdup(mntopt);
if (name == NULL)
return (ENOMEM);

for (ptr = name; ptr && *ptr; ptr++) {
if (*ptr == '=') {
*ptr = '\0';
value = ptr+1;
VERIFY3P(value, !=, NULL);
break;
}
}

for (opt = option_map; opt->name != NULL; opt++) {
if (strncmp(name, opt->name, strlen(name)) == 0) {
*mntflags |= opt->mntmask;
*zfsflags |= opt->zfsmask;
error = 0;
goto out;
}
}

if (!sloppy)
error = ENOENT;
out:
/* If required further process on the value may be done here */
free(name);
return (error);
}

/*
* Translate the mount option string in to MS_* mount flags for the
* kernel vfs. When sloppy is non-zero unknown options will be ignored
* otherwise they are considered fatal are copied in to badopt.
*/
static int
parse_options(char *mntopts, unsigned long *mntflags, unsigned long *zfsflags,
int sloppy, char *badopt, char *mtabopt)
{
int error = 0, quote = 0, flag = 0, count = 0;
char *ptr, *opt, *opts;

opts = strdup(mntopts);
if (opts == NULL)
return (ENOMEM);

*mntflags = 0;
opt = NULL;

/*
* Scan through all mount options which must be comma delimited.
* We must be careful to notice regions which are double quoted
* and skip commas in these regions. Each option is then checked
* to determine if it is a known option.
*/
for (ptr = opts; ptr && !flag; ptr++) {
if (opt == NULL)
opt = ptr;

if (*ptr == '"')
quote = !quote;

if (quote)
continue;

if (*ptr == '\0')
flag = 1;

if ((*ptr == ',') || (*ptr == '\0')) {
*ptr = '\0';

error = parse_option(opt, mntflags, zfsflags, sloppy);
if (error) {
strcpy(badopt, opt);
goto out;

}

if (!(*mntflags & MS_REMOUNT) &&
!(*zfsflags & ZS_ZFSUTIL)) {
if (count > 0)
strlcat(mtabopt, ",", MNT_LINE_MAX);

strlcat(mtabopt, opt, MNT_LINE_MAX);
count++;
}

opt = NULL;
}
}

out:
free(opts);
return (error);
}

/*
* Return the pool/dataset to mount given the name passed to mount. This
* is expected to be of the form pool/dataset, however may also refer to
Expand Down Expand Up @@ -345,34 +166,6 @@ mtab_update(char *dataset, char *mntpoint, char *type, char *mntopts)
return (MOUNT_SUCCESS);
}

static void
append_mntopt(const char *name, const char *val, char *mntopts,
char *mtabopt, boolean_t quote)
{
char tmp[MNT_LINE_MAX];

snprintf(tmp, MNT_LINE_MAX, quote ? ",%s=\"%s\"" : ",%s=%s", name, val);

if (mntopts)
strlcat(mntopts, tmp, MNT_LINE_MAX);

if (mtabopt)
strlcat(mtabopt, tmp, MNT_LINE_MAX);
}

static void
zfs_selinux_setcontext(zfs_handle_t *zhp, zfs_prop_t zpt, const char *name,
char *mntopts, char *mtabopt)
{
char context[ZFS_MAXPROPLEN];

if (zfs_prop_get(zhp, zpt, context, sizeof (context),
NULL, NULL, 0, B_FALSE) == 0) {
if (strcmp(context, "none") != 0)
append_mntopt(name, context, mntopts, mtabopt, B_TRUE);
}
}

int
main(int argc, char **argv)
{
Expand Down Expand Up @@ -449,7 +242,7 @@ main(int argc, char **argv)
}

/* validate mount options and set mntflags */
error = parse_options(mntopts, &mntflags, &zfsflags, sloppy,
error = zfs_parse_mount_options(mntopts, &mntflags, &zfsflags, sloppy,
badopt, mtabopt);
if (error) {
switch (error) {
Expand Down Expand Up @@ -502,32 +295,7 @@ main(int argc, char **argv)
return (MOUNT_USAGE);
}

/*
* Checks to see if the ZFS_PROP_SELINUX_CONTEXT exists
* if it does, create a tmp variable in case it's needed
* checks to see if the selinux context is set to the default
* if it is, allow the setting of the other context properties
* this is needed because the 'context' property overrides others
* if it is not the default, set the 'context' property
*/
if (zfs_prop_get(zhp, ZFS_PROP_SELINUX_CONTEXT, prop, sizeof (prop),
NULL, NULL, 0, B_FALSE) == 0) {
if (strcmp(prop, "none") == 0) {
zfs_selinux_setcontext(zhp, ZFS_PROP_SELINUX_FSCONTEXT,
MNTOPT_FSCONTEXT, mntopts, mtabopt);
zfs_selinux_setcontext(zhp, ZFS_PROP_SELINUX_DEFCONTEXT,
MNTOPT_DEFCONTEXT, mntopts, mtabopt);
zfs_selinux_setcontext(zhp,
ZFS_PROP_SELINUX_ROOTCONTEXT, MNTOPT_ROOTCONTEXT,
mntopts, mtabopt);
} else {
append_mntopt(MNTOPT_CONTEXT, prop,
mntopts, mtabopt, B_TRUE);
}
}

/* A hint used to determine an auto-mounted snapshot mount point */
append_mntopt(MNTOPT_MNTPOINT, mntpoint, mntopts, NULL, B_FALSE);
zfs_adjust_mount_options(zhp, mntpoint, mntopts, mtabopt);

/* treat all snapshots as legacy mount points */
if (zfs_get_type(zhp) == ZFS_TYPE_SNAPSHOT)
Expand Down
3 changes: 0 additions & 3 deletions cmd/zfs/zfs_main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7319,9 +7319,6 @@ unshare_unmount(int op, int argc, char **argv)
const char *mntarg = NULL;

uu_avl_remove(tree, node);
#ifndef __FreeBSD__
mntarg = node->un_zhp->zfs_name;
#endif
switch (op) {
case OP_SHARE:
if (zfs_unshareall_bytype(node->un_zhp,
Expand Down
7 changes: 7 additions & 0 deletions include/libzfs.h
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Original file line number Diff line number Diff line change
Expand Up @@ -803,6 +803,13 @@ extern int zfs_mount_at(zfs_handle_t *, const char *, int, const char *);
extern int zfs_unmount(zfs_handle_t *, const char *, int);
extern int zfs_unmountall(zfs_handle_t *, int);

#if defined(__linux__)
extern int zfs_parse_mount_options(char *mntopts, unsigned long *mntflags,
unsigned long *zfsflags, int sloppy, char *badopt, char *mtabopt);
extern void zfs_adjust_mount_options(zfs_handle_t *zhp, const char *mntpoint,
char *mntopts, char *mtabopt);
#endif

/*
* Share support functions.
*/
Expand Down
3 changes: 2 additions & 1 deletion include/libzfs_impl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -246,7 +246,8 @@ typedef struct differ_info {

extern proto_table_t proto_table[PROTO_END];

extern int do_mount(const char *src, const char *mntpt, char *opts, int flags);
extern int do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts,
int flags);
extern int do_unmount(const char *mntpt, int flags);
extern int zfs_mount_delegation_check(void);
extern int zfs_share_proto(zfs_handle_t *zhp, zfs_share_proto_t *proto);
Expand Down
2 changes: 1 addition & 1 deletion lib/libzfs/libzfs_mount.c
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Original file line number Diff line number Diff line change
Expand Up @@ -500,7 +500,7 @@ zfs_mount_at(zfs_handle_t *zhp, const char *options, int flags,
}

/* perform the mount */
rc = do_mount(zfs_get_name(zhp), mountpoint, mntopts, flags);
rc = do_mount(zhp, mountpoint, mntopts, flags);
if (rc) {
/*
* Generic errors are nasty, but there are just way too many
Expand Down
7 changes: 4 additions & 3 deletions lib/libzfs/os/freebsd/libzfs_zmount.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
#include <string.h>
#include <sys/mnttab.h>
#include <sys/errno.h>
#include <libzfs.h>

static void
build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val,
Expand Down Expand Up @@ -115,11 +116,11 @@ do_mount_(const char *spec, const char *dir, int mflag, char *fstype,
}

int
do_mount(const char *src, const char *mntpt, char *opts, int flags)
do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts, int flags)
{

return (do_mount_(src, mntpt, flags, MNTTYPE_ZFS, NULL, 0, opts,
sizeof (mntpt)));
return (do_mount_(zfs_get_name(zhp), mntpt, flags, MNTTYPE_ZFS, NULL, 0,
opts, sizeof (mntpt)));
}

int
Expand Down
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