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0b4d1b5853
The new snapdev dataset property may be set to control the
visibility of zvol snapshot devices. By default this value
is set to 'hidden' which will prevent zvol snapshots from
appearing under /dev/zvol/ and /dev/<dataset>/. When set to
'visible' all zvol snapshots for the dataset will be visible.
This functionality was largely added because when automatic
snapshoting is enabled large numbers of read-only zvol snapshots
will be created. When creating these devices the kernel will
attempt to read their partition tables, and blkid will attempt
to identify any filesystems on those partitions. This leads
to a variety of issues:
1) The zvol partition tables will be read in the context of
the `modprobe zfs` for automatically imported pools. This
is undesirable and should be done asynchronously, but for
now reducing the number of visible devices helps.
2) Udev expects to be able to complete its work for a new
block devices fairly quickly. When many zvol devices are
added at the same time this is no longer be true. It can
lead to udev timeouts and missing /dev/zvol links.
3) Simply having lots of devices in /dev/ can be aukward from
a management standpoint. Hidding the devices your unlikely
to ever use helps with this. Any snapshot device which is
needed can be made visible by changing the snapdev property.
NOTE: This patch changes the default behavior for zvols which
was effectively 'snapdev=visible'.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1235
Closes #945
Issue #956
Issue #756
54 lines
1.8 KiB
C
54 lines
1.8 KiB
C
/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License (the "License").
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* You may not use this file except in compliance with the License.
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*
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* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
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* or http://www.opensolaris.org/os/licensing.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
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* If applicable, add the following below this CDDL HEADER, with the
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* fields enclosed by brackets "[]" replaced with your own identifying
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* information: Portions Copyright [yyyy] [name of copyright owner]
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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) 2006, 2010, Oracle and/or its affiliates. All rights reserved.
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*/
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#ifndef _SYS_ZVOL_H
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#define _SYS_ZVOL_H
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#include <sys/zfs_context.h>
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#define ZVOL_OBJ 1ULL
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#define ZVOL_ZAP_OBJ 2ULL
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#ifdef _KERNEL
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extern int zvol_check_volsize(uint64_t volsize, uint64_t blocksize);
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extern int zvol_check_volblocksize(uint64_t volblocksize);
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extern int zvol_get_stats(objset_t *os, nvlist_t *nv);
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extern boolean_t zvol_is_zvol(const char *);
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extern void zvol_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx);
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extern int zvol_create_minor(const char *);
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extern int zvol_create_minors(const char *);
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extern int zvol_remove_minor(const char *);
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extern void zvol_remove_minors(const char *);
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extern int zvol_set_volsize(const char *, uint64_t);
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extern int zvol_set_volblocksize(const char *, uint64_t);
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extern int zvol_set_snapdev(const char *, uint64_t);
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extern int zvol_init(void);
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extern void zvol_fini(void);
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#endif /* _KERNEL */
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#endif /* _SYS_ZVOL_H */
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