zfs-program —
executes ZFS channel programs
zfs |
program
[-jn
]
[-t
instruction-limit
]
[-m
memory-limit
]
pool
script |
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:
The channel program given by
script will be run
on
pool, and any attempts to access or modify
other pools will cause an error.
-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.
A channel program can be invoked either from the command line, or via a library
call to
lzc_channel_program().
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.
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'
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.
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.
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
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}
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
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 guid) 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.
[optional] 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. Only user properties are
supported.
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.
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")
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
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