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loader: Add support for booting from a ZFS snapshot

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When booting from a snapshot we need to follow a different code path
to turn the objset ID into the name, and for forward lookups we need
to walk the parent's snapnames_zap.

With this, it is possible to set the pools BOOTFS property to a
snapshot and boot with a read-only filesystem of that snapshot.

Reviewed by:	tsoome, rew, imp
Sponsored By:	Beckhoff Automation GmbH & Co. KG
Sponsored By:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D38600
This commit is contained in:
Allan Jude 2022-11-26 18:11:13 +00:00
parent 21f2681828
commit a849842f51
1 changed files with 54 additions and 2 deletions
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56
stand/libsa/zfs/zfsimpl.c
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@ -3068,11 +3068,12 @@ zfs_rlookup(const spa_t *spa, uint64_t objnum, char *result)
char name[256];
char component[256];
uint64_t dir_obj, parent_obj, child_dir_zapobj;
dnode_phys_t child_dir_zap, dataset, dir, parent;
dnode_phys_t child_dir_zap, snapnames_zap, dataset, dir, parent;
dsl_dir_phys_t *dd;
dsl_dataset_phys_t *ds;
char *p;
int len;
boolean_t issnap = B_FALSE;
p = &name[sizeof(name) - 1];
*p = '\0';
@ -3083,6 +3084,8 @@ zfs_rlookup(const spa_t *spa, uint64_t objnum, char *result)
}
ds = (dsl_dataset_phys_t *)&dataset.dn_bonus;
dir_obj = ds->ds_dir_obj;
if (ds->ds_snapnames_zapobj == 0)
issnap = B_TRUE;
for (;;) {
if (objset_get_dnode(spa, spa->spa_mos, dir_obj, &dir) != 0)
@ -3098,6 +3101,34 @@ zfs_rlookup(const spa_t *spa, uint64_t objnum, char *result)
&parent) != 0)
return (EIO);
dd = (dsl_dir_phys_t *)&parent.dn_bonus;
if (issnap == B_TRUE) {
/*
* The dataset we are looking up is a snapshot
* the dir_obj is the parent already, we don't want
* the grandparent just yet. Reset to the parent.
*/
dd = (dsl_dir_phys_t *)&dir.dn_bonus;
/* Lookup the dataset to get the snapname ZAP */
if (objset_get_dnode(spa, spa->spa_mos,
dd->dd_head_dataset_obj, &dataset))
return (EIO);
ds = (dsl_dataset_phys_t *)&dataset.dn_bonus;
if (objset_get_dnode(spa, spa->spa_mos,
ds->ds_snapnames_zapobj, &snapnames_zap) != 0)
return (EIO);
/* Get the name of the snapshot */
if (zap_rlookup(spa, &snapnames_zap, component,
objnum) != 0)
return (EIO);
len = strlen(component);
p -= len;
memcpy(p, component, len);
--p;
*p = '@';
issnap = B_FALSE;
continue;
}
child_dir_zapobj = dd->dd_child_dir_zapobj;
if (objset_get_dnode(spa, spa->spa_mos, child_dir_zapobj,
&child_dir_zap) != 0)
@ -3127,9 +3158,11 @@ zfs_lookup_dataset(const spa_t *spa, const char *name, uint64_t *objnum)
{
char element[256];
uint64_t dir_obj, child_dir_zapobj;
dnode_phys_t child_dir_zap, dir;
dnode_phys_t child_dir_zap, snapnames_zap, dir, dataset;
dsl_dir_phys_t *dd;
dsl_dataset_phys_t *ds;
const char *p, *q;
boolean_t issnap = B_FALSE;
if (objset_get_dnode(spa, spa->spa_mos,
DMU_POOL_DIRECTORY_OBJECT, &dir))
@ -3160,6 +3193,25 @@ zfs_lookup_dataset(const spa_t *spa, const char *name, uint64_t *objnum)
p += strlen(p);
}
if (issnap == B_TRUE) {
if (objset_get_dnode(spa, spa->spa_mos,
dd->dd_head_dataset_obj, &dataset))
return (EIO);
ds = (dsl_dataset_phys_t *)&dataset.dn_bonus;
if (objset_get_dnode(spa, spa->spa_mos,
ds->ds_snapnames_zapobj, &snapnames_zap) != 0)
return (EIO);
/* Actual loop condition #2. */
if (zap_lookup(spa, &snapnames_zap, element,
sizeof (dir_obj), 1, &dir_obj) != 0)
return (ENOENT);
*objnum = dir_obj;
return (0);
} else if ((q = strchr(element, '@')) != NULL) {
issnap = B_TRUE;
element[q - element] = '\0';
p = q + 1;
}
child_dir_zapobj = dd->dd_child_dir_zapobj;
if (objset_get_dnode(spa, spa->spa_mos, child_dir_zapobj,
&child_dir_zap) != 0)