NAME¶

pmemblk_ctl_get(), pmemblk_ctl_set(), pmemblk_ctl_exec() - Query and modify libpmemblk internal behavior (EXPERIMENTAL)

SYNOPSIS¶

#include <libpmemblk.h>
int pmemblk_ctl_get(PMEMblkpool *pbp, const char *name, void *arg); (EXPERIMENTAL)
int pmemblk_ctl_set(PMEMblkpool *pbp, const char *name, void *arg); (EXPERIMENTAL)
int pmemblk_ctl_exec(PMEMblkpool *pbp, const char *name, void *arg); (EXPERIMENTAL)

DESCRIPTION¶

The pmemblk_ctl_get(), pmemblk_ctl_set() and pmemblk_ctl_exec() functions provide a uniform interface for querying and modifying the internal behavior of libpmemblk(7) through the control (CTL) namespace.

The name argument specifies an entry point as defined in the CTL namespace specification. The entry point description specifies whether the extra arg is required. Those two parameters together create a CTL query. The functions and the entry points are thread-safe unless indicated otherwise below. If there are special conditions for calling an entry point, they are explicitly stated in its description. The functions propagate the return value of the entry point. If either name or arg is invalid, -1 is returned.

If the provided ctl query is valid, the CTL functions will always return 0 on success and -1 on failure, unless otherwise specified in the entry point description.

See more in pmem_ctl(5) man page.

CTL NAMESPACE¶

prefault.at_create | rw | global | int | int | - | boolean

If set, every page of the pool will be touched and written to when the pool is created, in order to trigger page allocation and minimize the performance impact of pagefaults. Affects only the pmemblk_create() function.

Always returns 0.

prefault.at_open | rw | global | int | int | - | boolean

If set, every page of the pool will be touched and written to when the pool is opened, in order to trigger page allocation and minimize the performance impact of pagefaults. Affects only the pmemblk_open() function.

Always returns 0.

sds.at_create | rw | global | int | int | - | boolean

If set, force-enables or force-disables SDS feature during pool creation. Affects only the pmemblk_create() function. See pmempool_feature_query(3) for information about SDS (SHUTDOWN_STATE) feature.

Always returns 0.

copy_on_write.at_open | rw | global | int | int | - | boolean

If set, pool is mapped in such a way that modifications don't reach the underlying medium. From the user's perspective this means that when the pool is closed all changes are reverted. This feature is not supported for pools located on Device DAX.

Always returns 0.

CTL EXTERNAL CONFIGURATION¶

In addition to direct function call, each write entry point can also be set using two alternative methods.

The first method is to load a configuration directly from the PMEMBLK_CONF environment variable.

The second method of loading an external configuration is to set the PMEMBLK_CONF_FILE environment variable to point to a file that contains a sequence of ctl queries.

See more in pmem_ctl(5) man page.

SEE ALSO¶

libpmemblk(7), pmem_ctl(5) and <https://pmem.io>