Re: [Libguestfs] [libnbd PATCH v4 08/11] generator: Add `modifies_fd` flag to the [call] structure

On Wed, Aug 02, 2023 at 12:40:53PM +0000, Tage Johansson wrote: > Add a flag (`modifies_fd`) to the [call] structure in generator/API.ml > which is set to [true] if the handle call may do something with the > file descriptor. That is, it is [true] for all calls which are or may > call [aio_notify_*], including all synchronous commands like > [nbd_connect] or [nbd_opt_go]. > > The motivation for this is that the asynchronous handle in the Rust > bindings uses its own loop for polling, modifying the file descriptor > outside of this loop may cause unexpected behaviour. Including that the > handle may hang. All commands which set this flag to [true] will be > excluded from that handle. The asynchronous (`aio_*`) functions will be > used instead. Isn't this just saying that the call is synchronous? Rich.

> --- > generator/API.ml | 32 ++++++++++++++++++++++++++++++++ > generator/API.mli | 7 +++++++ > 2 files changed, 39 insertions(+) > > diff --git a/generator/API.ml b/generator/API.ml > index 42b9eec..6e1670d 100644 > --- a/generator/API.ml > +++ b/generator/API.ml > @@ -33,6 +33,7 @@ type call = { > is_locked : bool; > may_set_error : bool; > async_kind : async_kind option; > + modifies_fd: bool; > mutable first_version : int * int; > } > and arg = > @@ -274,6 +275,7 @@ let default_call = { args = []; optargs = []; ret = RErr; > permitted_states = []; > is_locked = true; may_set_error = true; > async_kind = None; > + modifies_fd = false; > first_version = (0, 0) } > > (* Calls. > @@ -1181,6 +1183,7 @@ Return true if option negotiation mode was enabled on this handle."; > default_call with > args = []; ret = RErr; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "end negotiation and move on to using an export"; > longdesc = "\ > Request that the server finish negotiation and move on to serving the > @@ -1208,6 +1211,7 @@ although older servers will instead have killed the connection."; > default_call with > args = []; ret = RErr; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "end negotiation and close the connection"; > longdesc = "\ > Request that the server finish negotiation, gracefully if possible, then > @@ -1221,6 +1225,7 @@ enabled option mode."; > default_call with > args = []; ret = RBool; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "request the server to initiate TLS"; > longdesc = "\ > Request that the server initiate a secure TLS connection, by > @@ -1259,6 +1264,7 @@ established, as reported by L<nbd_get_tls_negotiated(3)>."; > default_call with > args = []; ret = RBool; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "request the server to enable structured replies"; > longdesc = "\ > Request that the server use structured replies, by sending > @@ -1285,6 +1291,7 @@ later calls to this function return false."; > default_call with > args = [ Closure list_closure ]; ret = RInt; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "request the server to list all exports during negotiation"; > longdesc = "\ > Request that the server list all exports that it supports. This can > @@ -1326,6 +1333,7 @@ description is set with I<-D>."; > default_call with > args = []; ret = RErr; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "request the server for information about an export"; > longdesc = "\ > Request that the server supply information about the export name > @@ -1357,6 +1365,7 @@ corresponding L<nbd_opt_go(3)> would succeed."; > default_call with > args = [ Closure context_closure ]; ret = RInt; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "list available meta contexts, using implicit query list"; > longdesc = "\ > Request that the server list available meta contexts associated with > @@ -1412,6 +1421,7 @@ a server may send a lengthy list."; > default_call with > args = [ StringList "queries"; Closure context_closure ]; ret = RInt; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "list available meta contexts, using explicit query list"; > longdesc = "\ > Request that the server list available meta contexts associated with > @@ -1462,6 +1472,7 @@ a server may send a lengthy list."; > default_call with > args = [ Closure context_closure ]; ret = RInt; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "select specific meta contexts, using implicit query list"; > longdesc = "\ > Request that the server supply all recognized meta contexts > @@ -1521,6 +1532,7 @@ no contexts are reported, or may fail but have a non-empty list."; > default_call with > args = [ StringList "queries"; Closure context_closure ]; ret = RInt; > permitted_states = [ Negotiating ]; > + modifies_fd = true; > shortdesc = "select specific meta contexts, using explicit query list"; > longdesc = "\ > Request that the server supply all recognized meta contexts > @@ -1750,6 +1762,7 @@ parameter in NBD URIs is allowed."; > default_call with > args = [ String "uri" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect to NBD URI"; > longdesc = "\ > Connect (synchronously) to an NBD server and export by specifying > @@ -1928,6 +1941,7 @@ See L<nbd_get_uri(3)>."; > default_call with > args = [ Path "unixsocket" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect to NBD server over a Unix domain socket"; > longdesc = "\ > Connect (synchronously) over the named Unix domain socket (C<unixsocket>) > @@ -1941,6 +1955,7 @@ to an NBD server running on the same machine. > default_call with > args = [ UInt32 "cid"; UInt32 "port" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect to NBD server over AF_VSOCK protocol"; > longdesc = "\ > Connect (synchronously) over the C<AF_VSOCK> protocol from a > @@ -1961,6 +1976,7 @@ built on a system with vsock support, see L<nbd_supports_vsock(3)>. > default_call with > args = [ String "hostname"; String "port" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect to NBD server over a TCP port"; > longdesc = "\ > Connect (synchronously) to the NBD server listening on > @@ -1975,6 +1991,7 @@ such as C<\"10809\">. > default_call with > args = [ Fd "sock" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect directly to a connected socket"; > longdesc = "\ > Pass a connected socket C<sock> through which libnbd will talk > @@ -1996,6 +2013,7 @@ handle is closed. The caller must not use the socket in any way. > default_call with > args = [ StringList "argv" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect to NBD server command"; > longdesc = "\ > Run the command as a subprocess and connect to it over > @@ -2031,6 +2049,7 @@ is killed. > default_call with > args = [ StringList "argv" ]; ret = RErr; > permitted_states = [ Created ]; > + modifies_fd = true; > shortdesc = "connect using systemd socket activation"; > longdesc = "\ > Run the command as a subprocess and connect to it using > @@ -2404,6 +2423,7 @@ requests sizes. > optargs = [ OFlags ("flags", cmd_flags, Some []) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "read from the NBD server"; > longdesc = "\ > Issue a read command to the NBD server for the range starting > @@ -2443,6 +2463,7 @@ on failure." > optargs = [ OFlags ("flags", cmd_flags, Some ["DF"]) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "read from the NBD server"; > longdesc = "\ > Issue a read command to the NBD server for the range starting > @@ -2535,6 +2556,7 @@ on failure." > optargs = [ OFlags ("flags", cmd_flags, Some ["FUA"]) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "write to the NBD server"; > longdesc = "\ > Issue a write command to the NBD server, writing the data in > @@ -2568,6 +2590,7 @@ L<nbd_can_fua(3)>)." > args = []; optargs = [ OFlags ("flags", shutdown_flags, None) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "disconnect from the NBD server"; > longdesc = "\ > Issue the disconnect command to the NBD server. This is > @@ -2605,6 +2628,7 @@ A future version of the library may add new flags."; > default_call with > args = []; optargs = [ OFlags ("flags", cmd_flags, Some []) ]; ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "send flush command to the NBD server"; > longdesc = "\ > Issue the flush command to the NBD server. The function should > @@ -2625,6 +2649,7 @@ protocol extensions)." > optargs = [ OFlags ("flags", cmd_flags, Some ["FUA"]) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "send trim command to the NBD server"; > longdesc = "\ > Issue a trim command to the NBD server, which if supported > @@ -2656,6 +2681,7 @@ L<nbd_can_fua(3)>)." > optargs = [ OFlags ("flags", cmd_flags, Some []) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "send cache (prefetch) command to the NBD server"; > longdesc = "\ > Issue the cache (prefetch) command to the NBD server, which > @@ -2685,6 +2711,7 @@ protocol extensions)." > Some ["FUA"; "NO_HOLE"; "FAST_ZERO"]) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "send write zeroes command to the NBD server"; > longdesc = "\ > Issue a write zeroes command to the NBD server, which if supported > @@ -2723,6 +2750,7 @@ cannot do this, see L<nbd_can_fast_zero(3)>)." > optargs = [ OFlags ("flags", cmd_flags, Some ["REQ_ONE"]) ]; > ret = RErr; > permitted_states = [ Connected ]; > + modifies_fd = true; > shortdesc = "send block status command to the NBD server"; > longdesc = "\ > Issue the block status command to the NBD server. If > @@ -2789,6 +2817,7 @@ validate that the server obeyed the flag." > "poll", { > default_call with > args = [ Int "timeout" ]; ret = RInt; > + modifies_fd = true; > shortdesc = "poll the handle once"; > longdesc = "\ > This is a simple implementation of L<poll(2)> which is used > @@ -2810,6 +2839,7 @@ intended as something you would use."; > "poll2", { > default_call with > args = [Fd "fd"; Int "timeout" ]; ret = RInt; > + modifies_fd = true; > shortdesc = "poll the handle once, with fd"; > longdesc = "\ > This is the same as L<nbd_poll(3)>, but an additional > @@ -3493,6 +3523,7 @@ and invalidate the need to write more commands. > "aio_notify_read", { > default_call with > args = []; ret = RErr; > + modifies_fd = true; > shortdesc = "notify that the connection is readable"; > longdesc = "\ > Send notification to the state machine that the connection > @@ -3504,6 +3535,7 @@ connection is readable."; > "aio_notify_write", { > default_call with > args = []; ret = RErr; > + modifies_fd = true; > shortdesc = "notify that the connection is writable"; > longdesc = "\ > Send notification to the state machine that the connection > diff --git a/generator/API.mli b/generator/API.mli > index ff85849..4bf4468 100644 > --- a/generator/API.mli > +++ b/generator/API.mli > @@ -41,6 +41,13 @@ type call = { > if the function is asynchronous and in that case how one can check if > it has completed. *) > async_kind : async_kind option; > + (** A flag telling if the call may do something with the file descriptor. > + Some bindings needs exclusive access to the file descriptor and can not > + allow the user to call [aio_notify_read] or [aio_notify_write], neither > + directly nor indirectly from another call. So all calls that might trigger > + any of these functions to be called, including all synchronous commands > + like [pread] or [connect], should set this to [true]. *) > + modifies_fd : bool; > (** The first stable version that the symbol appeared in, for > example (1, 2) if the symbol was added in development cycle > 1.1.x and thus the first stable version was 1.2. This is > -- > 2.41.0