ZFS-PROGRAM(8) FreeBSD System Manager's Manual ZFS-PROGRAM(8)
NAME
zfs-program - execute ZFS channel programs
SYNOPSIS
zfs program [-jn] [-t instruction-limit] [-m memory-limit] pool script
[script arguments]
DESCRIPTION
The ZFS channel program interface allows ZFS administrative operations to
be run programmatically as a Lua script. The entire script is executed
atomically, with no other administrative operations taking effect
concurrently. A library of ZFS calls is made available to channel
program scripts. Channel programs may only be run with root privileges.
A modified version of the Lua 5.2 interpreter is used to run channel
program scripts. The Lua 5.2 manual can be found at
http://www.lua.org/manual/5.2/
The channel program given by script will be run on pool, and any attempts
to access or modify other pools will cause an error.
OPTIONS
-j Display channel program output in JSON format. When this flag is
specified and standard output is empty - channel program encountered
an error. The details of such an error will be printed to standard
error in plain text.
-n Executes a read-only channel program, which runs faster. The program
cannot change on-disk state by calling functions from the zfs.sync
submodule. The program can be used to gather information such as
properties and determining if changes would succeed (zfs.check.*).
Without this flag, all pending changes must be synced to disk before
a channel program can complete.
-t instruction-limit
Limit the number of Lua instructions to execute. If a channel
program executes more than the specified number of instructions, it
will be stopped and an error will be returned. The default limit is
10 million instructions, and it can be set to a maximum of 100
million instructions.
-m memory-limit
Memory limit, in bytes. If a channel program attempts to allocate
more memory than the given limit, it will be stopped and an error
returned. The default memory limit is 10 MB, and can be set to a
maximum of 100 MB.
All remaining argument strings will be passed directly to the Lua script
as described in the LUA INTERFACE section below.
LUA INTERFACE
A channel program can be invoked either from the command line, or via a
library call to lzc_channel_program().
Arguments
Arguments passed to the channel program are converted to a Lua table. If
invoked from the command line, extra arguments to the Lua script will be
accessible as an array stored in the argument table with the key 'argv':
args = ...
argv = args["argv"]
-- argv == {1="arg1", 2="arg2", ...}
If invoked from the libZFS interface, an arbitrary argument list can be
passed to the channel program, which is accessible via the same "..."
syntax in Lua:
args = ...
-- args == {"foo"="bar", "baz"={...}, ...}
Note that because Lua arrays are 1-indexed, arrays passed to Lua from the
libZFS interface will have their indices incremented by 1. That is, the
element in arr[0] in a C array passed to a channel program will be stored
in arr[1] when accessed from Lua.
Return Values
Lua return statements take the form:
return ret0, ret1, ret2, ...
Return statements returning multiple values are permitted internally in a
channel program script, but attempting to return more than one value from
the top level of the channel program is not permitted and will throw an
error. However, tables containing multiple values can still be returned.
If invoked from the command line, a return statement:
a = {foo="bar", baz=2}
return a
Will be output formatted as:
Channel program fully executed with return value:
return:
baz: 2
foo: 'bar'
Fatal Errors
If the channel program encounters a fatal error while running, a non-zero
exit status will be returned. If more information about the error is
available, a singleton list will be returned detailing the error:
error: "error string, including Lua stack trace"
If a fatal error is returned, the channel program may have not executed
at all, may have partially executed, or may have fully executed but
failed to pass a return value back to userland.
If the channel program exhausts an instruction or memory limit, a fatal
error will be generated and the program will be stopped, leaving the
program partially executed. No attempt is made to reverse or undo any
operations already performed. Note that because both the instruction
count and amount of memory used by a channel program are deterministic
when run against the same inputs and filesystem state, as long as a
channel program has run successfully once, you can guarantee that it will
finish successfully against a similar size system.
If a channel program attempts to return too large a value, the program
will fully execute but exit with a nonzero status code and no return
value.
Note: ZFS API functions do not generate Fatal Errors when correctly
invoked, they return an error code and the channel program continues
executing. See the ZFS API section below for function-specific details
on error return codes.
Lua to C Value Conversion
When invoking a channel program via the libZFS interface, it is necessary
to translate arguments and return values from Lua values to their C
equivalents, and vice-versa.
There is a correspondence between nvlist values in C and Lua tables. A
Lua table which is returned from the channel program will be recursively
converted to an nvlist, with table values converted to their natural
equivalents:
string -> string
number -> int64
boolean -> boolean_value
nil -> boolean (no value)
table -> nvlist
Likewise, table keys are replaced by string equivalents as follows:
string -> no change
number -> signed decimal string ("%lld")
boolean -> "true" | "false"
Any collision of table key strings (for example, the string "true" and a
true boolean value) will cause a fatal error.
Lua numbers are represented internally as signed 64-bit integers.
LUA STANDARD LIBRARY
The following Lua built-in base library functions are available:
assert rawlen collectgarbage rawget
error rawset getmetatable select
ipairs setmetatable next tonumber
pairs tostring rawequal type
All functions in the coroutine, string, and table built-in submodules are
also available. A complete list and documentation of these modules is
available in the Lua manual.
The following functions base library functions have been disabled and are
not available for use in channel programs:
dofile loadfile load pcall print xpcall
ZFS API
Function Arguments
Each API function takes a fixed set of required positional arguments and
optional keyword arguments. For example, the destroy function takes a
single positional string argument (the name of the dataset to destroy)
and an optional "defer" keyword boolean argument. When using parentheses
to specify the arguments to a Lua function, only positional arguments can
be used:
zfs.sync.destroy("rpool@snap")
To use keyword arguments, functions must be called with a single argument
that is a Lua table containing entries mapping integers to positional
arguments and strings to keyword arguments:
zfs.sync.destroy({1="rpool@snap", defer=true})
The Lua language allows curly braces to be used in place of parenthesis
as syntactic sugar for this calling convention:
zfs.sync.snapshot{"rpool@snap", defer=true}
Function Return Values
If an API function succeeds, it returns 0. If it fails, it returns an
error code and the channel program continues executing. API functions do
not generate Fatal Errors except in the case of an unrecoverable internal
file system error.
In addition to returning an error code, some functions also return extra
details describing what caused the error. This extra description is
given as a second return value, and will always be a Lua table, or Nil if
no error details were returned. Different keys will exist in the error
details table depending on the function and error case. Any such
function may be called expecting a single return value:
errno = zfs.sync.promote(dataset)
Or, the error details can be retrieved:
errno, details = zfs.sync.promote(dataset)
if (errno == EEXIST) then
assert(details ~= Nil)
list_of_conflicting_snapshots = details
end
The following global aliases for API function error return codes are
defined for use in channel programs:
EPERM ECHILD ENODEV ENOSPC ENOENT EAGAIN ENOTDIR
ESPIPE ESRCH ENOMEM EISDIR EROFS EINTR EACCES
EINVAL EMLINK EIO EFAULT ENFILE EPIPE ENXIO
ENOTBLK EMFILE EDOM E2BIG EBUSY ENOTTY ERANGE
ENOEXEC EEXIST ETXTBSY EDQUOT EBADF EXDEV EFBIG
API Functions
For detailed descriptions of the exact behavior of any ZFS administrative
operations, see the main zfs(8) manual page.
zfs.debug(msg)
Record a debug message in the zfs_dbgmsg log. A log of these
messages can be printed via mdb's "::zfs_dbgmsg" command, or can be
monitored live by running
dtrace -n 'zfs-dbgmsg{trace(stringof(arg0))}'
msg (string) Debug message to be printed.
zfs.exists(dataset)
Returns true if the given dataset exists, or false if it doesn't. A
fatal error will be thrown if the dataset is not in the target pool.
That is, in a channel program running on rpool,
zfs.exists("rpool/nonexistent_fs") returns false, but
zfs.exists("somepool/fs_that_may_exist") will error.
dataset (string) Dataset to check for existence. Must be in the
target pool.
zfs.get_prop(dataset, property)
Returns two values. First, a string, number or table containing the
property value for the given dataset. Second, a string containing
the source of the property (i.e. the name of the dataset in which it
was set or nil if it is readonly). Throws a Lua error if the dataset
is invalid or the property doesn't exist. Note that Lua only
supports int64 number types whereas ZFS number properties are uint64.
This means very large values (like GUIDs) may wrap around and appear
negative.
dataset (string) Filesystem or snapshot path to retrieve properties
from.
property (string) Name of property to retrieve. All filesystem,
snapshot and volume properties are supported
except for mounted and iscsioptions. Also
supports the written@snap and written#bookmark
properties and the <user|group><quota|used>@id
properties, though the id must be in numeric form.
zfs.sync submodule
The sync submodule contains functions that modify the on-disk state.
They are executed in "syncing context".
The available sync submodule functions are as follows:
zfs.sync.destroy(dataset, [defer=true|false])
Destroy the given dataset. Returns 0 on successful destroy, or a
nonzero error code if the dataset could not be destroyed (for
example, if the dataset has any active children or clones).
dataset (string) Filesystem or snapshot to be destroyed.
[defer (boolean)] Valid only for destroying snapshots. If
set to true, and the snapshot has holds or
clones, allows the snapshot to be marked
for deferred deletion rather than failing.
zfs.sync.inherit(dataset, property)
Clears the specified property in the given dataset, causing it to
be inherited from an ancestor, or restored to the default if no
ancestor property is set. The zfs inherit -S option has not been
implemented. Returns 0 on success, or a nonzero error code if
the property could not be cleared.
dataset (string) Filesystem or snapshot containing the
property to clear.
property (string) The property to clear. Allowed properties
are the same as those for the zfs inherit
command.
zfs.sync.promote(dataset)
Promote the given clone to a filesystem. Returns 0 on successful
promotion, or a nonzero error code otherwise. If EEXIST is
returned, the second return value will be an array of the clone's
snapshots whose names collide with snapshots of the parent
filesystem.
dataset (string) Clone to be promoted.
zfs.sync.rollback(filesystem)
Rollback to the previous snapshot for a dataset. Returns 0 on
successful rollback, or a nonzero error code otherwise.
Rollbacks can be performed on filesystems or zvols, but not on
snapshots or mounted datasets. EBUSY is returned in the case
where the filesystem is mounted.
filesystem (string) Filesystem to rollback.
zfs.sync.set_prop(dataset, property, value)
Sets the given property on a dataset. Currently only user
properties are supported. Returns 0 if the property was set, or
a nonzero error code otherwise.
dataset (string) The dataset where the property will be set.
property (string) The property to set.
value (string) The value of the property to be set.
zfs.sync.snapshot(dataset)
Create a snapshot of a filesystem. Returns 0 if the snapshot was
successfully created, and a nonzero error code otherwise.
Note: Taking a snapshot will fail on any pool older than legacy
version 27. To enable taking snapshots from ZCP scripts, the
pool must be upgraded.
dataset (string) Name of snapshot to create.
zfs.sync.bookmark(source, newbookmark)
Create a bookmark of an existing source snapshot or bookmark.
Returns 0 if the new bookmark was successfully created, and a
nonzero error code otherwise.
Note: Bookmarking requires the corresponding pool feature to be
enabled.
source (string) Full name of the existing snapshot or
bookmark.
newbookmark (string) Full name of the new bookmark.
zfs.check submodule
For each function in the zfs.sync submodule, there is a corresponding
zfs.check function which performs a "dry run" of the same operation.
Each takes the same arguments as its zfs.sync counterpart and returns
0 if the operation would succeed, or a non-zero error code if it
would fail, along with any other error details. That is, each has
the same behavior as the corresponding sync function except for
actually executing the requested change. For example,
zfs.check.destroy("fs") returns 0 if zfs.sync.destroy("fs") would
successfully destroy the dataset.
The available zfs.check functions are:
zfs.check.destroy(dataset, [defer=true|false])
zfs.check.promote(dataset)
zfs.check.rollback(filesystem)
zfs.check.set_property(dataset, property, value)
zfs.check.snapshot(dataset)
zfs.list submodule
The zfs.list submodule provides functions for iterating over datasets
and properties. Rather than returning tables, these functions act as
Lua iterators, and are generally used as follows:
for child in zfs.list.children("rpool") do
...
end
The available zfs.list functions are:
zfs.list.clones(snapshot)
Iterate through all clones of the given snapshot.
snapshot (string) Must be a valid snapshot path in the current
pool.
zfs.list.snapshots(dataset)
Iterate through all snapshots of the given dataset. Each
snapshot is returned as a string containing the full dataset
name, e.g. "pool/fs@snap".
dataset (string) Must be a valid filesystem or volume.
zfs.list.children(dataset)
Iterate through all direct children of the given dataset. Each
child is returned as a string containing the full dataset name,
e.g. "pool/fs/child".
dataset (string) Must be a valid filesystem or volume.
zfs.list.bookmarks(dataset)
Iterate through all bookmarks of the given dataset. Each
bookmark is returned as a string containing the full dataset
name, e.g. "pool/fs#bookmark".
dataset (string) Must be a valid filesystem or volume.
zfs.list.holds(snapshot)
Iterate through all user holds on the given snapshot. Each hold
is returned as a pair of the hold's tag and the timestamp (in
seconds since the epoch) at which it was created.
snapshot (string) Must be a valid snapshot.
zfs.list.properties(dataset)
An alias for zfs.list.user_properties (see relevant entry).
dataset (string) Must be a valid filesystem, snapshot, or
volume.
zfs.list.user_properties(dataset)
Iterate through all user properties for the given dataset. For
each step of the iteration, output the property name, its value,
and its source. Throws a Lua error if the dataset is invalid.
dataset (string) Must be a valid filesystem, snapshot, or
volume.
zfs.list.system_properties(dataset)
Returns an array of strings, the names of the valid system (non-
user defined) properties for the given dataset. Throws a Lua
error if the dataset is invalid.
dataset (string) Must be a valid filesystem, snapshot or
volume.
EXAMPLES
Example 1
The following channel program recursively destroys a filesystem and all
its snapshots and children in a naive manner. Note that this does not
involve any error handling or reporting.
function destroy_recursive(root)
for child in zfs.list.children(root) do
destroy_recursive(child)
end
for snap in zfs.list.snapshots(root) do
zfs.sync.destroy(snap)
end
zfs.sync.destroy(root)
end
destroy_recursive("pool/somefs")
Example 2
A more verbose and robust version of the same channel program, which
properly detects and reports errors, and also takes the dataset to
destroy as a command line argument, would be as follows:
succeeded = {}
failed = {}
function destroy_recursive(root)
for child in zfs.list.children(root) do
destroy_recursive(child)
end
for snap in zfs.list.snapshots(root) do
err = zfs.sync.destroy(snap)
if (err ~= 0) then
failed[snap] = err
else
succeeded[snap] = err
end
end
err = zfs.sync.destroy(root)
if (err ~= 0) then
failed[root] = err
else
succeeded[root] = err
end
end
args = ...
argv = args["argv"]
destroy_recursive(argv[1])
results = {}
results["succeeded"] = succeeded
results["failed"] = failed
return results
Example 3
The following function performs a forced promote operation by attempting
to promote the given clone and destroying any conflicting snapshots.
function force_promote(ds)
errno, details = zfs.check.promote(ds)
if (errno == EEXIST) then
assert(details ~= Nil)
for i, snap in ipairs(details) do
zfs.sync.destroy(ds .. "@" .. snap)
end
elseif (errno ~= 0) then
return errno
end
return zfs.sync.promote(ds)
end
FreeBSD 13.1-RELEASE-p6 May 27, 2021 FreeBSD 13.1-RELEASE-p6
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