On 4/21/23 11:20, Richard W.M. Jones wrote:
> See: https://github.com/libguestfs/nbdkit/issues/21
>
> Tested by applying the following patch to the example plugin and
> running it with verbose enabled:
>
> --- a/plugins/rust/examples/ramdisk.rs
> +++ b/plugins/rust/examples/ramdisk.rs
> @@ -43,6 +43,12 @@ struct RamDisk {
> }
>
> impl Server for RamDisk {
> + fn after_fork() -> Result<()> {
> + // A place to start background threads.
> + eprintln!("forked");
> + Ok(())
> + }
> +
> fn get_size(&self) -> Result<i64> {
> Ok(DISK.lock().unwrap().len() as i64)
> }
> @@ -76,4 +82,4 @@ impl Server for RamDisk {
> }
> }
>
> -plugin!(RamDisk {thread_model, write_at});
> +plugin!(RamDisk {thread_model, write_at, after_fork});
I *think* diffs embedded in commit messages are best quoted somehow (or
at least indented); I vaguely recall "naked" diffs in the commit message
confusing git-am.
I've not written a line of Rust thus far, so I'll let Alan review the patch.
Laszlo
> ---
> plugins/rust/src/lib.rs | 23 ++++++++++++++++-
> plugins/rust/tests/common/mod.rs | 1 +
> plugins/rust/tests/full_featured.rs | 39 +++++++++++++++++++++++++++++
> 3 files changed, 62 insertions(+), 1 deletion(-)
>
> diff --git a/plugins/rust/src/lib.rs b/plugins/rust/src/lib.rs
> index a5b88e851..fc7b28454 100644
> --- a/plugins/rust/src/lib.rs
> +++ b/plugins/rust/src/lib.rs
> @@ -143,6 +143,7 @@ mod unreachable {
> pub(super) fn thread_model() -> Result<ThreadModel> { unreachable!() }
> }
>
> +static mut AFTER_FORK: fn() -> Result<()> = unreachable::config_complete;
> static mut CONFIG: fn(k: &str, v: &str) -> Result<()> = unreachable::config;
> static mut CONFIG_COMPLETE: fn() -> Result<()> =
> unreachable::config_complete;
> static mut CONFIG_HELP: Vec<u8> = Vec::new();
> @@ -315,6 +316,16 @@ impl ExtentHandle {
> mod ffi {
> use super::*;
>
> + pub(super) extern fn after_fork() -> c_int {
> + match unsafe { AFTER_FORK() } {
> + Ok(()) => 0,
> + Err(e) => {
> + set_error(e);
> + -1
> + }
> + }
> + }
> +
> macro_rules! can_method {
> ( $meth:ident ) => {
> pub(super) extern fn $meth(h: *mut c_void) -> c_int {
> @@ -584,6 +595,12 @@ mod ffi {
> // We want the argument names to show up without underscores in the API docs
> #[allow(unused_variables)]
> pub trait Server {
> + /// This optional callback is called before the server starts serving.
> + ///
> + /// It is called after the server forks and changes directory. If
> + /// a plugin needs to create background threads it should do so here.
> + fn after_fork() -> Result<()> where Self: Sized { unimplemented!() }
> +
> /// Indicates that the client intends to make further accesses to the
> given
> /// data region.
> ///
> @@ -900,6 +917,7 @@ macro_rules! opt_method {
> #[doc(hidden)]
> #[derive(Default)]
> pub struct Builder {
> + pub after_fork: bool,
> pub cache: bool,
> pub can_cache: bool,
> pub can_extents: bool,
> @@ -938,6 +956,7 @@ impl Builder {
> CONFIG_COMPLETE = S::config_complete;
> DUMP_PLUGIN = S::dump_plugin;
> GET_READY = S::get_ready;
> + AFTER_FORK = S::after_fork;
> LOAD = S::load;
> OPEN = S::open;
> PRECONNECT = S::preconnect;
> @@ -1021,7 +1040,8 @@ impl Builder {
> thread_model: opt_method!(self, thread_model),
> can_fast_zero: opt_method!(self, can_fast_zero),
> preconnect: opt_method!(self, preconnect),
> - get_ready: opt_method!(self, get_ready)
> + get_ready: opt_method!(self, get_ready),
> + after_fork: opt_method!(self, after_fork)
> };
> // Leak the memory to C. NBDKit will never give it back.
> Box::into_raw(Box::new(plugin))
> @@ -1191,6 +1211,7 @@ pub struct Plugin {
> pub can_fast_zero: Option<extern fn (h: *mut c_void) -> c_int>,
> pub preconnect: Option<extern fn(readonly: c_int) -> c_int>,
> pub get_ready: Option<extern fn() -> c_int>,
> + pub after_fork: Option<extern fn() -> c_int>,
> }
>
> /// Register your plugin with NBDKit.
> diff --git a/plugins/rust/tests/common/mod.rs
> b/plugins/rust/tests/common/mod.rs
> index de26c89fc..77c987a1f 100644
> --- a/plugins/rust/tests/common/mod.rs
> +++ b/plugins/rust/tests/common/mod.rs
> @@ -50,6 +50,7 @@ mock!{
> pub Server {}
> #[allow(dead_code)]
> impl Server for Server {
> + fn after_fork() -> Result<()> where Self: Sized;
> fn cache(&self, count: u32, offset: u64) -> Result<()>;
> fn can_cache(&self) -> Result<CacheFlags>;
> fn can_extents(&self) -> Result<bool>;
> diff --git a/plugins/rust/tests/full_featured.rs
> b/plugins/rust/tests/full_featured.rs
> index d5f02e064..87a0256e0 100644
> --- a/plugins/rust/tests/full_featured.rs
> +++ b/plugins/rust/tests/full_featured.rs
> @@ -46,6 +46,7 @@ static mut PLUGIN: Option<*const Plugin> = None;
> static INIT: Once = Once::new();
>
> plugin!(MockServer{
> + after_fork,
> cache,
> can_cache,
> can_extents,
> @@ -539,6 +540,44 @@ mod get_ready {
> }
> }
>
> +mod after_fork {
> + use super::*;
> +
> + #[test]
> + fn einval() {
> + initialize();
> + let _m = MOCK_SERVER_MTX.lock().unwrap();
> +
> + let after_fork_ctx = MockServer::after_fork_context();
> + after_fork_ctx.expect()
> + .returning(|| Err(Error::new(libc::EINVAL, "foo is required")));
> +
> + let pluginp = unsafe { PLUGIN.unwrap()};
> + let plugin = unsafe {&*pluginp};
> +
> + let after_fork = plugin.after_fork.as_ref().unwrap();
> + assert_eq!( -1, after_fork());
> + ERRNO.with(|e| assert_eq!(libc::EINVAL, *e.borrow()));
> + ERRMSG.with(|e| assert_eq!("foo is required", *e.borrow()));
> + }
> +
> + #[test]
> + fn ok() {
> + initialize();
> + let _m = MOCK_SERVER_MTX.lock().unwrap();
> +
> + let after_fork_ctx = MockServer::after_fork_context();
> + after_fork_ctx.expect()
> + .returning(|| Ok(()));
> +
> + let pluginp = unsafe { PLUGIN.unwrap()};
> + let plugin = unsafe {&*pluginp};
> +
> + let after_fork = plugin.after_fork.as_ref().unwrap();
> + assert_eq!( 0, after_fork());
> + }
> +}
> +
> can_method!(is_rotational, expect_is_rotational);
>
> unload_like!(load, load_context);
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