Allow mounting datasets more than once
Currently mounting an already mounted zfs dataset results in an error, whereas it is typically allowed with other filesystems. This causes some bad interactions with mount namespaces. Take this sequence for example: - Create a dataset - Create a snapshot of the dataset - Create a clone of the snapshot - Create a new mount namespace - Rename the original dataset The rename results in unmounting and remounting the clone in the original mount namespace, however the remount fails because the dataset is still mounted in the new mount namespace. (Note that this means the mount in the new mount namespace is never being unmounted, so perhaps the unmount/remount of the clone isn't actually necessary.) The problem here is a result of the way mounting is implemented in the kernel module. Since it is not mounting block devices it uses mount_nodev() instead of the usual mount_bdev(). However, mount_nodev() is written for filesystems for which each mount is a new instance (i.e. a new super block), and zfs should be able to detect when a mount request can be satisfied using an existing super block. Change zpl_mount() to call sget() directly with it's own test callback. Passing the objset_t object as the fs data allows checking if a superblock already exists for the dataset, and in that case we just need to return a new reference for the sb's root dentry. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Tom Caputi <tcaputi@datto.com> Signed-off-by: Alek Pinchuk <apinchuk@datto.com> Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Closes #5796 Closes #7207
This commit is contained in:
Seth Forshee
Brian Behlendorf
parent
1e37dee03f
commit
93b43af10d
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@ -0,0 +1,28 @@
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dnl #
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dnl # 2.6.38 API change
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dnl # The .get_sb callback has been replaced by a .mount callback
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dnl # in the file_system_type structure.
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dnl #
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AC_DEFUN([ZFS_AC_KERNEL_FST_MOUNT], [
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AC_MSG_CHECKING([whether fst->mount() exists])
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ZFS_LINUX_TRY_COMPILE([
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#include <linux/fs.h>
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static struct dentry *
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mount(struct file_system_type *fs_type, int flags,
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const char *osname, void *data) {
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struct dentry *d = NULL;
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return (d);
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}
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static struct file_system_type fst __attribute__ ((unused)) = {
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.mount = mount,
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};
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],[
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],[
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_FST_MOUNT, 1, [fst->mount() exists])
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],[
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AC_MSG_RESULT(no)
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])
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])
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@ -1,20 +0,0 @@
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dnl #
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dnl # 2.6.39 API change
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dnl # The .get_sb callback has been replaced by a .mount callback
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dnl # in the file_system_type structure. When using the new
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dnl # interface the caller must now use the mount_nodev() helper.
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dnl # This updated callback and helper no longer pass the vfsmount.
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dnl #
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AC_DEFUN([ZFS_AC_KERNEL_MOUNT_NODEV],
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[AC_MSG_CHECKING([whether mount_nodev() is available])
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ZFS_LINUX_TRY_COMPILE_SYMBOL([
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#include <linux/fs.h>
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], [
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mount_nodev(NULL, 0, NULL, NULL);
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], [mount_nodev], [fs/super.c], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_MOUNT_NODEV, 1, [mount_nodev() is available])
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], [
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AC_MSG_RESULT(no)
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])
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])
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@ -103,7 +103,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
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ZFS_AC_KERNEL_TRUNCATE_SETSIZE
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ZFS_AC_KERNEL_6ARGS_SECURITY_INODE_INIT_SECURITY
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ZFS_AC_KERNEL_CALLBACK_SECURITY_INODE_INIT_SECURITY
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ZFS_AC_KERNEL_MOUNT_NODEV
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ZFS_AC_KERNEL_FST_MOUNT
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ZFS_AC_KERNEL_SHRINK
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ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID
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ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD
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@ -182,6 +182,30 @@ zpl_bdi_destroy(struct super_block *sb)
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}
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#endif
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/*
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* 4.14 adds SB_* flag definitions, define them to MS_* equivalents
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* if not set.
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*/
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#ifndef SB_RDONLY
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#define SB_RDONLY MS_RDONLY
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#endif
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#ifndef SB_SILENT
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#define SB_SILENT MS_SILENT
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#endif
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#ifndef SB_ACTIVE
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#define SB_ACTIVE MS_ACTIVE
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#endif
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#ifndef SB_POSIXACL
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#define SB_POSIXACL MS_POSIXACL
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#endif
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#ifndef SB_MANDLOCK
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#define SB_MANDLOCK MS_MANDLOCK
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#endif
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/*
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* 2.6.38 API change,
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* LOOKUP_RCU flag introduced to distinguish rcu-walk from ref-walk cases.
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@ -248,14 +248,61 @@ zpl_fill_super(struct super_block *sb, void *data, int silent)
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return (error);
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}
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#ifdef HAVE_MOUNT_NODEV
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static int
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zpl_test_super(struct super_block *s, void *data)
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{
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zfsvfs_t *zfsvfs = s->s_fs_info;
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objset_t *os = data;
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if (zfsvfs == NULL)
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return (0);
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return (os == zfsvfs->z_os);
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}
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static struct super_block *
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zpl_mount_impl(struct file_system_type *fs_type, int flags, zfs_mnt_t *zm)
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{
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struct super_block *s;
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objset_t *os;
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int err;
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err = dmu_objset_hold(zm->mnt_osname, FTAG, &os);
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if (err)
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return (ERR_PTR(-err));
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s = zpl_sget(fs_type, zpl_test_super, set_anon_super, flags, os);
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dmu_objset_rele(os, FTAG);
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if (IS_ERR(s))
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return (ERR_CAST(s));
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if (s->s_root == NULL) {
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err = zpl_fill_super(s, zm, flags & SB_SILENT ? 1 : 0);
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if (err) {
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deactivate_locked_super(s);
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return (ERR_PTR(err));
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}
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s->s_flags |= SB_ACTIVE;
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} else if ((flags ^ s->s_flags) & SB_RDONLY) {
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deactivate_locked_super(s);
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return (ERR_PTR(-EBUSY));
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}
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return (s);
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}
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#ifdef HAVE_FST_MOUNT
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static struct dentry *
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zpl_mount(struct file_system_type *fs_type, int flags,
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const char *osname, void *data)
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{
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zfs_mnt_t zm = { .mnt_osname = osname, .mnt_data = data };
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return (mount_nodev(fs_type, flags, &zm, zpl_fill_super));
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struct super_block *sb = zpl_mount_impl(fs_type, flags, &zm);
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if (IS_ERR(sb))
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return (ERR_CAST(sb));
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return (dget(sb->s_root));
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}
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#else
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static int
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@ -264,9 +311,15 @@ zpl_get_sb(struct file_system_type *fs_type, int flags,
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{
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zfs_mnt_t zm = { .mnt_osname = osname, .mnt_data = data };
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return (get_sb_nodev(fs_type, flags, &zm, zpl_fill_super, mnt));
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struct super_block *sb = zpl_mount_impl(fs_type, flags, &zm);
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if (IS_ERR(sb))
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return (PTR_ERR(sb));
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(void) simple_set_mnt(mnt, sb);
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return (0);
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}
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#endif /* HAVE_MOUNT_NODEV */
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#endif /* HAVE_FST_MOUNT */
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static void
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zpl_kill_sb(struct super_block *sb)
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@ -333,10 +386,10 @@ const struct super_operations zpl_super_operations = {
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struct file_system_type zpl_fs_type = {
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.owner = THIS_MODULE,
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.name = ZFS_DRIVER,
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#ifdef HAVE_MOUNT_NODEV
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#ifdef HAVE_FST_MOUNT
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.mount = zpl_mount,
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#else
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.get_sb = zpl_get_sb,
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#endif /* HAVE_MOUNT_NODEV */
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#endif /* HAVE_FST_MOUNT */
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.kill_sb = zpl_kill_sb,
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};
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@ -174,7 +174,7 @@ tests = ['zfs_mount_001_pos', 'zfs_mount_002_pos', 'zfs_mount_003_pos',
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'zfs_mount_004_pos', 'zfs_mount_005_pos', 'zfs_mount_007_pos',
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'zfs_mount_008_pos', 'zfs_mount_009_neg', 'zfs_mount_010_neg',
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'zfs_mount_011_neg', 'zfs_mount_012_neg', 'zfs_mount_all_001_pos',
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'zfs_mount_encrypted', 'zfs_mount_remount']
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'zfs_mount_encrypted', 'zfs_mount_remount', 'zfs_multi_mount']
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tags = ['functional', 'cli_root', 'zfs_mount']
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[tests/functional/cli_root/zfs_program]
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@ -16,7 +16,8 @@ dist_pkgdata_SCRIPTS = \
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zfs_mount_012_neg.ksh \
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zfs_mount_encrypted.ksh \
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zfs_mount_all_001_pos.ksh \
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zfs_mount_remount.ksh
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zfs_mount_remount.ksh \
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zfs_multi_mount.ksh
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dist_pkgdata_DATA = \
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zfs_mount.cfg \
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@ -0,0 +1,104 @@
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#!/bin/ksh -p
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#
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# CDDL HEADER START
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#
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# This file and its contents are supplied under the terms of the
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# Common Development and Distribution License ("CDDL"), version 1.0.
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# You may only use this file in accordance with the terms of version
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# 1.0 of the CDDL.
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#
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# A full copy of the text of the CDDL should have accompanied this
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# source. A copy is of the CDDL is also available via the Internet
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# at http://www.illumos.org/license/CDDL.
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#
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# CDDL HEADER END
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#
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#
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# Copyright(c) 2018 Datto Inc.
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#
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. $STF_SUITE/include/libtest.shlib
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#
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# DESCRIPTION:
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# Verify multi mount functionality
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#
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# STRATEGY:
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# 1. Create fs
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# 2. Create and hold open file in filesystem
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# 3. Lazy unmount
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# 4. Verify remounting fs that was lazily unmounted is possible
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# 5. Verify multiple mounts of the same dataset are possible
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# 6. Verify bind mount doesn't prevent rename
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#
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verify_runnable "both"
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function cleanup
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{
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ismounted $MNTPFS && log_must umount $MNTPFS
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ismounted $MNTPFS2 && log_must umount $MNTPFS2
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ismounted $MNTPFS3 && log_must umount $MNTPFS3
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ismounted $MNTPFS4 && log_must umount $MNTPFS4
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ismounted $RENAMEMNT && log_must umount $RENAMEMNT
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datasetexists $TESTDS && log_must destroy_dataset "$TESTDS" "-f"
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}
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log_onexit cleanup
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log_assert "Verify multiple mounts into one namespace are possible"
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# 1. Create fs
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TESTDS="$TESTPOOL/multi-mount-test"
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log_must zfs create $TESTDS
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# 2. Create and hold open file in filesystem
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MNTPFS="$(get_prop mountpoint $TESTDS)"
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FILENAME="$MNTPFS/file"
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log_must mkfile 128k $FILENAME
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log_must exec 9<> $FILENAME # open file
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# 3. Lazy umount
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log_must umount -l $MNTPFS
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if [ -f $FILENAME ]; then
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log_fail "Lazy unmount failed"
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fi
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# 4. Verify remounting fs that was lazily unmounted is possible
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log_must zfs mount $TESTDS
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if [ ! -f $FILENAME ]; then
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log_fail "Lazy remount failed"
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fi
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log_must exec 9>&- # close fd
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# 5. Verify multiple mounts of the same dataset are possible
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MNTPFS2="$MNTPFS-second"
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FILENAME="$MNTPFS2/file"
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log_must mkdir $MNTPFS2
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log_must mount -t zfs -o zfsutil $TESTDS $MNTPFS2
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if [ ! -f $FILENAME ]; then
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log_fail "First multi mount failed"
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fi
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MNTPFS3="$MNTPFS-third"
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FILENAME="$MNTPFS3/file"
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log_must mkdir $MNTPFS3
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log_must mount -t zfs -o zfsutil $TESTDS $MNTPFS3
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if [ ! -f $FILENAME ]; then
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log_fail "Second multi mount failed"
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fi
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# 6. Verify bind mount doesn't prevent rename
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RENAMEFS="$TESTDS-newname"
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MNTPFS4="$MNTPFS-fourth"
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log_must mkdir $MNTPFS4
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log_must mount --bind $MNTPFS $MNTPFS4
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log_must zfs rename $TESTDS $RENAMEFS
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RENAMEMNT="$(get_prop mountpoint $RENAMEFS)"
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FILENAME="$RENAMEMNT/file"
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if [ ! -f $FILENAME ]; then
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log_fail "Rename failed"
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fi
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log_must zfs rename $RENAMEFS $TESTDS
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log_pass "Multiple mounts are possible"
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