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When a namespace property is changed via zfs set, libzfs remounts the filesystem to propagate the new VFS mount flags. The current approach uses mount(2) with MS_REMOUNT, which reads all namespace properties from ZFS and applies them together. This has two problems: 1. Linux VFS resets unspecified per-mount flags on remount. If an administrator sets a temporary flag (e.g. mount -o remount,noatime), a subsequent zfs set on any namespace property clobbers it. 2. Two concurrent zfs set operations on different namespace properties can overwrite each other's mount flags. Additionally, legacy datasets (mountpoint=legacy) were never remounted on namespace property changes since zfs_is_mountable() returns false for them. Add zfs_mount_setattr() which uses mount_setattr(2) to selectively update only the mount flags that correspond to the changed property. For legacy datasets, /proc/mounts is iterated to update all mountpoints. On kernels without mount_setattr (ENOSYS), non-legacy datasets fall back to a full remount; legacy mounts are skipped to avoid clobbering temporary flags. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Ameer Hamza <ahamza@ixsystems.com> Closes #18257
28 lines
646 B
Plaintext
28 lines
646 B
Plaintext
dnl # SPDX-License-Identifier: CDDL-1.0
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dnl #
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dnl # Check for mount_setattr() and struct mount_attr availability
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dnl #
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AC_DEFUN([ZFS_AC_CONFIG_USER_MOUNT_SETATTR], [
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AC_CHECK_FUNC([mount_setattr], [
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AC_MSG_CHECKING([for struct mount_attr])
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AC_COMPILE_IFELSE([
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AC_LANG_PROGRAM([[
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#include <sys/mount.h>
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]], [[
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struct mount_attr attr = {
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.attr_set = MOUNT_ATTR_RDONLY,
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.attr_clr = MOUNT_ATTR_NOEXEC,
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};
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(void) attr;
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]])
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], [
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AC_MSG_RESULT([yes])
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AC_DEFINE([HAVE_MOUNT_SETATTR], [1],
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[mount_setattr() and struct mount_attr
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are 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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])
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