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d17b298a48
fish-shell/src/exec.cpp
ridiculousfish d17b298a48 Factor out the code that executes a builtin from exec_job() 
Very early work on untangling the exec_job spaghetti.
2017-12-22 13:41:29 -08:00

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// Functions for executing a program.
//
// Some of the code in this file is based on code from the Glibc manual, though the changes
// performed have been massive.
#include "config.h"
#include <errno.h>
#include <fcntl.h>
#ifdef HAVE_SIGINFO_H
#include <siginfo.h>
#endif
#include <signal.h>
#ifdef HAVE_SPAWN_H
#include <spawn.h>
#endif
#include <stdio.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
#include <algorithm>
#include <functional>
#include <map>
#include <memory>
#include <string>
#include <type_traits>
#include <vector>
#include "builtin.h"
#include "common.h"
#include "env.h"
#include "exec.h"
#include "fallback.h" // IWYU pragma: keep
#include "function.h"
#include "io.h"
#include "parse_tree.h"
#include "parser.h"
#include "postfork.h"
#include "proc.h"
#include "reader.h"
#include "signal.h"
#include "wutil.h" // IWYU pragma: keep
/// File descriptor redirection error message.
#define FD_ERROR _(L"An error occurred while redirecting file descriptor %d")
/// File descriptor redirection error message.
#define WRITE_ERROR _(L"An error occurred while writing output")
/// File redirection error message.
#define FILE_ERROR _(L"An error occurred while redirecting file '%s'")
/// Base open mode to pass to calls to open.
#define OPEN_MASK 0666
/// Called in a forked child.
static void exec_write_and_exit(int fd, const char *buff, size_t count, int status) {
if (write_loop(fd, buff, count) == -1) {
debug(0, WRITE_ERROR);
wperror(L"write");
exit_without_destructors(status);
}
exit_without_destructors(status);
}
void exec_close(int fd) {
ASSERT_IS_MAIN_THREAD();
// This may be called in a child of fork(), so don't allocate memory.
if (fd < 0) {
debug(0, L"Called close on invalid file descriptor ");
return;
}
while (close(fd) == -1) {
if (errno != EINTR) {
debug(1, FD_ERROR, fd);
wperror(L"close");
break;
}
}
}
int exec_pipe(int fd[2]) {
ASSERT_IS_MAIN_THREAD();
int res;
while ((res = pipe(fd))) {
if (errno != EINTR) {
return res; // caller will call wperror
}
}
debug(4, L"Created pipe using fds %d and %d", fd[0], fd[1]);
// Pipes ought to be cloexec. Pipes are dup2'd the corresponding fds; the resulting fds are not
// cloexec.
set_cloexec(fd[0]);
set_cloexec(fd[1]);
return res;
}
/// Returns true if the redirection is a file redirection to a file other than /dev/null.
static bool redirection_is_to_real_file(const io_data_t *io) {
bool result = false;
if (io != NULL && io->io_mode == IO_FILE) {
// It's a file redirection. Compare the path to /dev/null.
const io_file_t *io_file = static_cast<const io_file_t *>(io);
const char *path = io_file->filename_cstr;
if (strcmp(path, "/dev/null") != 0) {
// It's not /dev/null.
result = true;
}
}
return result;
}
static bool chain_contains_redirection_to_real_file(const io_chain_t &io_chain) {
bool result = false;
for (size_t idx = 0; idx < io_chain.size(); idx++) {
const io_data_t *io = io_chain.at(idx).get();
if (redirection_is_to_real_file(io)) {
result = true;
break;
}
}
return result;
}
/// Returns the interpreter for the specified script. Returns NULL if file is not a script with a
/// shebang.
char *get_interpreter(const char *command, char *interpreter, size_t buff_size) {
// OK to not use CLO_EXEC here because this is only called after fork.
int fd = open(command, O_RDONLY);
if (fd >= 0) {
size_t idx = 0;
while (idx + 1 < buff_size) {
char ch;
ssize_t amt = read(fd, &ch, sizeof ch);
if (amt <= 0) break;
if (ch == '\n') break;
interpreter[idx++] = ch;
}
interpreter[idx++] = '\0';
close(fd);
}
if (strncmp(interpreter, "#! /", 4) == 0) {
return interpreter + 3;
} else if (strncmp(interpreter, "#!/", 3) == 0) {
return interpreter + 2;
}
return NULL;
}
/// This function is executed by the child process created by a call to fork(). It should be called
/// after \c setup_child_process. It calls execve to replace the fish process image with the command
/// specified in \c p. It never returns. Called in a forked child! Do not allocate memory, etc.
static void safe_launch_process(process_t *p, const char *actual_cmd, const char *const *cargv,
const char *const *cenvv) {
UNUSED(p);
int err;
// debug( 1, L"exec '%ls'", p->argv[0] );
// This function never returns, so we take certain liberties with constness.
char *const *envv = const_cast<char *const *>(cenvv);
char *const *argv = const_cast<char *const *>(cargv);
execve(actual_cmd, argv, envv);
err = errno;
// Something went wrong with execve, check for a ":", and run /bin/sh if encountered. This is a
// weird predecessor to the shebang that is still sometimes used since it is supported on
// Windows. OK to not use CLO_EXEC here because this is called after fork and the file is
// immediately closed.
int fd = open(actual_cmd, O_RDONLY);
if (fd >= 0) {
char begin[1] = {0};
ssize_t amt_read = read(fd, begin, 1);
close(fd);
if ((amt_read == 1) && (begin[0] == ':')) {
// Relaunch it with /bin/sh. Don't allocate memory, so if you have more args than this,
// update your silly script! Maybe this should be changed to be based on ARG_MAX
// somehow.
char sh_command[] = "/bin/sh";
char *argv2[128];
argv2[0] = sh_command;
for (size_t i = 1; i < sizeof argv2 / sizeof *argv2; i++) {
argv2[i] = argv[i - 1];
if (argv2[i] == NULL) break;
}
execve(sh_command, argv2, envv);
}
}
errno = err;
safe_report_exec_error(errno, actual_cmd, argv, envv);
exit_without_destructors(STATUS_EXEC_FAIL);
}
/// This function is similar to launch_process, except it is not called after a fork (i.e. it only
/// calls exec) and therefore it can allocate memory.
static void launch_process_nofork(process_t *p) {
ASSERT_IS_MAIN_THREAD();
ASSERT_IS_NOT_FORKED_CHILD();
null_terminated_array_t<char> argv_array;
convert_wide_array_to_narrow(p->get_argv_array(), &argv_array);
const char *const *envv = env_export_arr();
char *actual_cmd = wcs2str(p->actual_cmd);
// Ensure the terminal modes are what they were before we changed them.
restore_term_mode();
// Bounce to launch_process. This never returns.
safe_launch_process(p, actual_cmd, argv_array.get(), envv);
}
/// Check if the IO redirection chains contains redirections for the specified file descriptor.
static int has_fd(const io_chain_t &d, int fd) { return io_chain_get(d, fd).get() != NULL; }
/// Close a list of fds.
static void io_cleanup_fds(const std::vector<int> &opened_fds) {
std::for_each(opened_fds.begin(), opened_fds.end(), close);
}
/// Make a copy of the specified io redirection chain, but change file redirection into fd
/// redirection. This makes the redirection chain suitable for use as block-level io, since the file
/// won't be repeatedly reopened for every command in the block, which would reset the cursor
/// position.
///
/// \return true on success, false on failure. Returns the output chain and opened_fds by reference.
static bool io_transmogrify(const io_chain_t &in_chain, io_chain_t *out_chain,
std::vector<int> *out_opened_fds) {
ASSERT_IS_MAIN_THREAD();
assert(out_chain != NULL && out_opened_fds != NULL);
assert(out_chain->empty());
// Just to be clear what we do for an empty chain.
if (in_chain.empty()) {
return true;
}
bool success = true;
// Make our chain of redirections.
io_chain_t result_chain;
// In the event we can't finish transmorgrifying, we'll have to close all the files we opened.
std::vector<int> opened_fds;
for (size_t idx = 0; idx < in_chain.size(); idx++) {
const shared_ptr<io_data_t> &in = in_chain.at(idx);
shared_ptr<io_data_t> out; // gets allocated via new
switch (in->io_mode) {
case IO_PIPE:
case IO_FD:
case IO_BUFFER:
case IO_CLOSE: {
// These redirections don't need transmogrification. They can be passed through.
out = in;
break;
}
case IO_FILE: {
// Transmogrify file redirections.
int fd;
io_file_t *in_file = static_cast<io_file_t *>(in.get());
if ((fd = open(in_file->filename_cstr, in_file->flags, OPEN_MASK)) == -1) {
debug(1, FILE_ERROR, in_file->filename_cstr);
wperror(L"open");
success = false;
break;
}
opened_fds.push_back(fd);
out.reset(new io_fd_t(in->fd, fd, false));
break;
}
}
if (out.get() != NULL) result_chain.push_back(out);
// Don't go any further if we failed.
if (!success) {
break;
}
}
// Now either return success, or clean up.
if (success) {
*out_chain = std::move(result_chain);
*out_opened_fds = std::move(opened_fds);
} else {
result_chain.clear();
io_cleanup_fds(opened_fds);
}
return success;
}
/// Morph an io redirection chain into redirections suitable for passing to eval, call eval, and
/// clean up morphed redirections.
///
/// \param def the code to evaluate, or the empty string if none
/// \param node_offset the offset of the node to evalute, or NODE_OFFSET_INVALID
/// \param block_type the type of block to push on evaluation
/// \param ios the io redirections to be performed on this block
static void internal_exec_helper(parser_t &parser, const wcstring &def, node_offset_t node_offset,
enum block_type_t block_type, const io_chain_t &ios) {
// If we have a valid node offset, then we must not have a string to execute.
assert(node_offset == NODE_OFFSET_INVALID || def.empty());
io_chain_t morphed_chain;
std::vector<int> opened_fds;
bool transmorgrified = io_transmogrify(ios, &morphed_chain, &opened_fds);
// Did the transmogrification fail - if so, set error status and return.
if (!transmorgrified) {
proc_set_last_status(STATUS_EXEC_FAIL);
return;
}
if (node_offset == NODE_OFFSET_INVALID) {
parser.eval(def, morphed_chain, block_type);
} else {
parser.eval_block_node(node_offset, morphed_chain, block_type);
}
morphed_chain.clear();
io_cleanup_fds(opened_fds);
job_reap(0);
}
// Returns whether we can use posix spawn for a given process in a given job. Per
// https://github.com/fish-shell/fish-shell/issues/364 , error handling for file redirections is too
// difficult with posix_spawn, so in that case we use fork/exec.
//
// Furthermore, to avoid the race between the caller calling tcsetpgrp() and the client checking the
// foreground process group, we don't use posix_spawn if we're going to foreground the process. (If
// we use fork(), we can call tcsetpgrp after the fork, before the exec, and avoid the race).
static bool can_use_posix_spawn_for_job(const job_t *job, const process_t *process) {
if (job->get_flag(JOB_CONTROL)) { //!OCLINT(collapsible if statements)
// We are going to use job control; therefore when we launch this job it will get its own
// process group ID. But will it be foregrounded?
if (job->get_flag(JOB_TERMINAL) && job->get_flag(JOB_FOREGROUND)) {
// It will be foregrounded, so we will call tcsetpgrp(), therefore do not use
// posix_spawn.
return false;
}
}
// Now see if we have a redirection involving a file. The only one we allow is /dev/null, which
// we assume will not fail.
bool result = true;
if (chain_contains_redirection_to_real_file(job->block_io_chain()) ||
chain_contains_redirection_to_real_file(process->io_chain())) {
result = false;
}
return result;
}
void internal_exec(job_t *j, const io_chain_t &&all_ios) {
// Do a regular launch - but without forking first...
signal_block();
// setup_child_process makes sure signals are properly set up. It will also call
// signal_unblock.
// PCA This is for handling exec. Passing all_ios here matches what fish 2.0.0 and 1.x did.
// It's known to be wrong - for example, it means that redirections bound for subsequent
// commands in the pipeline will apply to exec. However, using exec in a pipeline doesn't
// really make sense, so I'm not trying to fix it here.
if (!setup_child_process(0, all_ios)) {
// Decrement SHLVL as we're removing ourselves from the shell "stack".
auto shlvl_var = env_get(L"SHLVL", ENV_GLOBAL | ENV_EXPORT);
wcstring shlvl_str = L"0";
if (shlvl_var) {
long shlvl = fish_wcstol(shlvl_var->as_string().c_str());
if (!errno && shlvl > 0) {
shlvl_str = to_string<long>(shlvl - 1);
}
}
env_set_one(L"SHLVL", ENV_GLOBAL | ENV_EXPORT, shlvl_str);
// launch_process _never_ returns.
launch_process_nofork(j->processes.front().get());
} else {
j->set_flag(JOB_CONSTRUCTED, true);
j->processes.front()->completed = 1;
return;
}
}
/// Execute an internal builtin. Given a parser, a job within that parser, and a process within that
/// job corresponding to a builtin, execute the builtin with the given streams. If pipe_read is set,
/// assign stdin to it; otherwise infer stdin from the IO chain. unblock_previous is a hack used to
/// prevent jobs from finishing; see commit cdb72b7024.
/// return true on success, false if there is an exec error.
static bool exec_internal_builtin_proc(parser_t &parser, job_t *j, process_t *p,
const io_pipe_t *pipe_read, const io_chain_t &proc_io_chain,
io_streams_t &streams,
const std::function<void(void)> &unblock_previous) {
assert(p->type == INTERNAL_BUILTIN && "Process must be a builtin");
int local_builtin_stdin = STDIN_FILENO;
bool close_stdin = false;
// If this is the first process, check the io redirections and see where we should
// be reading from.
if (pipe_read) {
local_builtin_stdin = pipe_read->pipe_fd[0];
} else if (const auto in = proc_io_chain.get_io_for_fd(STDIN_FILENO)) {
switch (in->io_mode) {
case IO_FD: {
const io_fd_t *in_fd = static_cast<const io_fd_t *>(in.get());
// Ignore user-supplied fd redirections from an fd other than the
// standard ones. e.g. in source <&3 don't actually read from fd 3,
// which is internal to fish. We still respect this redirection in
// that we pass it on as a block IO to the code that source runs,
// and therefore this is not an error. Non-user supplied fd
// redirections come about through transmogrification, and we need
// to respect those here.
if (!in_fd->user_supplied || (in_fd->old_fd >= 0 && in_fd->old_fd < 3)) {
local_builtin_stdin = in_fd->old_fd;
}
break;
}
case IO_PIPE: {
const io_pipe_t *in_pipe = static_cast<const io_pipe_t *>(in.get());
local_builtin_stdin = in_pipe->pipe_fd[0];
break;
}
case IO_FILE: {
// Do not set CLO_EXEC because child needs access.
const io_file_t *in_file = static_cast<const io_file_t *>(in.get());
local_builtin_stdin = open(in_file->filename_cstr, in_file->flags, OPEN_MASK);
if (local_builtin_stdin == -1) {
debug(1, FILE_ERROR, in_file->filename_cstr);
wperror(L"open");
} else {
close_stdin = true;
}
break;
}
case IO_CLOSE: {
// FIXME: When requesting that stdin be closed, we really don't do
// anything. How should this be handled?
local_builtin_stdin = -1;
break;
}
default: {
local_builtin_stdin = -1;
debug(1, _(L"Unknown input redirection type %d"), in->io_mode);
break;
}
}
}
if (local_builtin_stdin == -1) return false;
// Determine if we have a "direct" redirection for stdin.
bool stdin_is_directly_redirected;
if (!p->is_first_in_job) {
// We must have a pipe
stdin_is_directly_redirected = true;
} else {
// We are not a pipe. Check if there is a redirection local to the process
// that's not IO_CLOSE.
const shared_ptr<const io_data_t> stdin_io = io_chain_get(p->io_chain(), STDIN_FILENO);
stdin_is_directly_redirected = stdin_io && stdin_io->io_mode != IO_CLOSE;
}
streams.stdin_fd = local_builtin_stdin;
streams.out_is_redirected = has_fd(proc_io_chain, STDOUT_FILENO);
streams.err_is_redirected = has_fd(proc_io_chain, STDERR_FILENO);
streams.stdin_is_directly_redirected = stdin_is_directly_redirected;
streams.io_chain = &proc_io_chain;
// Since this may be the foreground job, and since a builtin may execute another
// foreground job, we need to pretend to suspend this job while running the
// builtin, in order to avoid a situation where two jobs are running at once.
//
// The reason this is done here, and not by the relevant builtins, is that this
// way, the builtin does not need to know what job it is part of. It could
// probably figure that out by walking the job list, but it seems more robust to
// make exec handle things.
const int fg = j->get_flag(JOB_FOREGROUND);
j->set_flag(JOB_FOREGROUND, false);
// Main loop may need to perform a blocking read from previous command's output.
// Make sure read source is not blocked.
unblock_previous();
p->status = builtin_run(parser, p->get_argv(), streams);
// Restore the fg flag, which is temporarily set to false during builtin
// execution so as not to confuse some job-handling builtins.
j->set_flag(JOB_FOREGROUND, fg);
// If stdin has been redirected, close the redirection stream.
if (close_stdin) {
exec_close(local_builtin_stdin);
}
return true; // "success"
}
void exec_job(parser_t &parser, job_t *j) {
pid_t pid = 0;
// Set to true if something goes wrong while exec:ing the job, in which case the cleanup code
// will kick in.
bool exec_error = false;
bool needs_keepalive = false;
process_t keepalive;
CHECK(j, );
CHECK_BLOCK();
// If fish was invoked with -n or --no-execute, then no_exec will be set and we do nothing.
if (no_exec) {
return;
}
debug(4, L"Exec job '%ls' with id %d", j->command_wcstr(), j->job_id);
// Verify that all IO_BUFFERs are output. We used to support a (single, hacked-in) magical input
// IO_BUFFER used by fish_pager, but now the claim is that there are no more clients and it is
// removed. This assertion double-checks that.
size_t stdout_read_limit = 0;
const io_chain_t all_ios = j->all_io_redirections();
for (size_t idx = 0; idx < all_ios.size(); idx++) {
const shared_ptr<io_data_t> &io = all_ios.at(idx);
if ((io->io_mode == IO_BUFFER)) {
io_buffer_t *io_buffer = static_cast<io_buffer_t *>(io.get());
assert(!io_buffer->is_input);
stdout_read_limit = io_buffer->get_buffer_limit();
}
}
if (j->processes.front()->type == INTERNAL_EXEC) {
internal_exec(j, std::move(all_ios));
DIE("this should be unreachable");
}
// We may have block IOs that conflict with fd redirections. For example, we may have a command
// with a redireciton like <&3; we may also have chosen 3 as the fd for our pipe. Ensure we have
// no conflicts.
for (size_t i = 0; i < all_ios.size(); i++) {
io_data_t *io = all_ios.at(i).get();
if (io->io_mode == IO_BUFFER) {
io_buffer_t *io_buffer = static_cast<io_buffer_t *>(io);
if (!io_buffer->avoid_conflicts_with_io_chain(all_ios)) {
// We could not avoid conflicts, probably due to fd exhaustion. Mark an error.
exec_error = true;
job_mark_process_as_failed(j, j->processes.front().get());
break;
}
}
}
// See if we need to create a group keepalive process. This is a process that we create to make
// sure that the process group doesn't die accidentally, and is often needed when a
// builtin/block/function is inside a pipeline, since that usually means we have to wait for one
// program to exit before continuing in the pipeline, causing the group leader to exit.
if (j->get_flag(JOB_CONTROL) && !exec_error) {
for (const process_ptr_t &p : j->processes) {
if (p->type != EXTERNAL && (!p->is_last_in_job || !p->is_first_in_job)) {
needs_keepalive = true;
break;
}
}
}
if (needs_keepalive) {
// Call fork. No need to wait for threads since our use is confined and simple.
keepalive.pid = execute_fork(false);
if (keepalive.pid == 0) {
// Child
keepalive.pid = getpid();
child_set_group(j, &keepalive);
pause();
exit_without_destructors(0);
} else {
// Parent
debug(2, L"Fork #%d, pid %d: keepalive fork for '%ls'", g_fork_count, keepalive.pid,
j->command_wcstr());
set_child_group(j, keepalive.pid);
}
}
// This loop loops over every process_t in the job, starting it as appropriate. This turns out
// to be rather complex, since a process_t can be one of many rather different things.
//
// The loop also has to handle pipelining between the jobs.
//
// We can have up to three pipes "in flight" at a time:
//
// 1. The pipe the current process should read from (courtesy of the previous process)
// 2. The pipe that the current process should write to
// 3. The pipe that the next process should read from (courtesy of us)
//
// We are careful to set these to -1 when closed, so if we exit the loop abruptly, we can still
// close them.
bool pgrp_set = false;
// This is static since processes can block on input/output across jobs the main exec_job loop
// is only ever run in a single thread, so this is OK.
static pid_t blocked_pid = -1;
int pipe_current_read = -1, pipe_current_write = -1, pipe_next_read = -1;
for (std::unique_ptr<process_t> &unique_p : j->processes) {
if (exec_error) {
break;
}
process_t *const p = unique_p.get();
// The IO chain for this process. It starts with the block IO, then pipes, and then gets any
// from the process.
io_chain_t process_net_io_chain = j->block_io_chain();
// "Consume" any pipe_next_read by making it current.
assert(pipe_current_read == -1);
pipe_current_read = pipe_next_read;
pipe_next_read = -1;
// See if we need a pipe.
const bool pipes_to_next_command = !p->is_last_in_job;
// Set to true if we end up forking for this process.
bool child_forked = false;
bool child_spawned = false;
bool block_child = true;
// The pipes the current process write to and read from. Unfortunately these can't be just
// allocated on the stack, since j->io wants shared_ptr.
//
// The write pipe (destined for stdout) needs to occur before redirections. For example,
// with a redirection like this:
//
// `foo 2>&1 | bar`
//
// what we want to happen is this:
//
// dup2(pipe, stdout)
// dup2(stdout, stderr)
//
// so that stdout and stderr both wind up referencing the pipe.
//
// The read pipe (destined for stdin) is more ambiguous. Imagine a pipeline like this:
//
// echo alpha | cat < beta.txt
//
// Should cat output alpha or beta? bash and ksh output 'beta', tcsh gets it right and
// complains about ambiguity, and zsh outputs both (!). No shells appear to output 'alpha',
// so we match bash here. That would mean putting the pipe first, so that it gets trumped by
// the file redirection.
//
// However, eval does this:
//
// echo "begin; $argv "\n" ;end <&3 3<&-" | source 3<&0
//
// which depends on the redirection being evaluated before the pipe. So the write end of the
// pipe comes first, the read pipe of the pipe comes last. See issue #966.
shared_ptr<io_pipe_t> pipe_write;
shared_ptr<io_pipe_t> pipe_read;
// Write pipe goes first.
if (pipes_to_next_command) {
pipe_write.reset(new io_pipe_t(p->pipe_write_fd, false));
process_net_io_chain.push_back(pipe_write);
}
// The explicit IO redirections associated with the process.
process_net_io_chain.append(p->io_chain());
// Read pipe goes last.
if (!p->is_first_in_job) {
pipe_read.reset(new io_pipe_t(p->pipe_read_fd, true));
// Record the current read in pipe_read.
pipe_read->pipe_fd[0] = pipe_current_read;
process_net_io_chain.push_back(pipe_read);
}
// This call is used so the global environment variable array is regenerated, if needed,
// before the fork. That way, we avoid a lot of duplicate work where EVERY child would need
// to generate it, since that result would not get written back to the parent. This call
// could be safely removed, but it would result in slightly lower performance - at least on
// uniprocessor systems.
if (p->type == EXTERNAL) {
// Apply universal barrier so we have the most recent uvar changes
if (!get_proc_had_barrier()) {
set_proc_had_barrier(true);
env_universal_barrier();
}
env_export_arr();
}
// Set up fds that will be used in the pipe.
if (pipes_to_next_command) {
// debug( 1, L"%ls|%ls" , p->argv[0], p->next->argv[0]);
int local_pipe[2] = {-1, -1};
if (exec_pipe(local_pipe) == -1) {
debug(1, PIPE_ERROR);
wperror(L"pipe");
exec_error = true;
job_mark_process_as_failed(j, p);
break;
}
// Ensure our pipe fds not conflict with any fd redirections. E.g. if the process is
// like 'cat <&5' then fd 5 must not be used by the pipe.
if (!pipe_avoid_conflicts_with_io_chain(local_pipe, all_ios)) {
// We failed. The pipes were closed for us.
wperror(L"dup");
exec_error = true;
job_mark_process_as_failed(j, p);
break;
}
// This tells the redirection about the fds, but the redirection does not close them.
assert(local_pipe[0] >= 0);
assert(local_pipe[1] >= 0);
memcpy(pipe_write->pipe_fd, local_pipe, sizeof(int) * 2);
// Record our pipes. The fds should be negative to indicate that we aren't overwriting
// an fd we failed to close.
assert(pipe_current_write == -1);
pipe_current_write = local_pipe[1];
assert(pipe_next_read == -1);
pipe_next_read = local_pipe[0];
}
// This is the IO buffer we use for storing the output of a block or function when it is in
// a pipeline.
shared_ptr<io_buffer_t> block_output_io_buffer;
// Used to SIGCONT the previously SIGSTOP'd process so the main loop or next command in job
// can read from its output.
auto unblock_previous = [&j]() {
// We've already called waitpid after forking the child, so we've guaranteed that
// they're already SIGSTOP'd. Otherwise we'd be risking a deadlock because we can call
// SIGCONT before they've actually stopped, and they'll remain suspended indefinitely.
if (blocked_pid != -1) {
debug(2, L"Unblocking process %d.\n", blocked_pid);
kill(blocked_pid, SIGCONT);
blocked_pid = -1;
}
};
// This is the io_streams we pass to internal builtins.
std::unique_ptr<io_streams_t> builtin_io_streams(new io_streams_t(stdout_read_limit));
auto do_fork = [&j, &p, &pid, &exec_error, &process_net_io_chain, &block_child,
&child_forked](bool drain_threads, const char *fork_type,
std::function<void()> child_action) -> bool {
pid = execute_fork(drain_threads);
if (pid == 0) {
// This is the child process. Setup redirections, print correct output to
// stdout and stderr, and then exit.
p->pid = getpid();
blocked_pid = -1;
child_set_group(j, p);
// Make child processes pause after executing setup_child_process() to give
// down-chain commands in the job a chance to join their process group and read
// their pipes. The process will be resumed when the next command in the chain is
// started.
if (block_child) {
kill(p->pid, SIGSTOP);
}
// The parent will wake us up when we're ready to execute.
setup_child_process(p, process_net_io_chain);
child_action();
DIE("Child process returned control to do_fork lambda!");
} else {
if (pid < 0) {
debug(1, L"Failed to fork %s!\n", fork_type);
job_mark_process_as_failed(j, p);
exec_error = true;
return false;
}
// This is the parent process. Store away information on the child, and
// possibly give it control over the terminal.
debug(2, L"Fork #%d, pid %d: %s for '%ls'", g_fork_count, pid, fork_type,
p->argv0());
child_forked = true;
if (block_child) {
debug(2, L"Blocking process %d waiting for next command in chain.\n", pid);
}
p->pid = pid;
}
return true;
};
// Helper routine executed by INTERNAL_FUNCTION and INTERNAL_BLOCK_NODE to make sure an
// output buffer exists in case there is another command in the job chain that will be
// reading from this command's output.
auto verify_buffer_output = [&]() {
if (!p->is_last_in_job) {
// Be careful to handle failure, e.g. too many open fds.
block_output_io_buffer = io_buffer_t::create(STDOUT_FILENO, all_ios);
if (block_output_io_buffer.get() == NULL) {
exec_error = true;
job_mark_process_as_failed(j, p);
} else {
// This looks sketchy, because we're adding this io buffer locally - they
// aren't in the process or job redirection list. Therefore select_try won't
// be able to read them. However we call block_output_io_buffer->read()
// below, which reads until EOF. So there's no need to select on this.
process_net_io_chain.push_back(block_output_io_buffer);
}
}
};
switch (p->type) {
case INTERNAL_FUNCTION: {
const wcstring func_name = p->argv0();
wcstring def;
bool function_exists = function_get_definition(func_name, &def);
bool shadow_scope = function_get_shadow_scope(func_name);
const std::map<wcstring, env_var_t> inherit_vars =
function_get_inherit_vars(func_name);
if (!function_exists) {
debug(0, _(L"Unknown function '%ls'"), p->argv0());
break;
}
function_block_t *fb =
parser.push_block<function_block_t>(p, func_name, shadow_scope);
function_prepare_environment(func_name, p->get_argv() + 1, inherit_vars);
parser.forbid_function(func_name);
verify_buffer_output();
if (!exec_error) {
internal_exec_helper(parser, def, NODE_OFFSET_INVALID, TOP,
process_net_io_chain);
}
parser.allow_function();
parser.pop_block(fb);
break;
}
case INTERNAL_BLOCK_NODE: {
verify_buffer_output();
if (!exec_error) {
internal_exec_helper(parser, wcstring(), p->internal_block_node, TOP,
process_net_io_chain);
}
break;
}
case INTERNAL_BUILTIN: {
if (!exec_internal_builtin_proc(parser, j, p, pipe_read.get(), process_net_io_chain,
*builtin_io_streams, unblock_previous)) {
exec_error = true;
}
break;
}
case EXTERNAL:
// External commands are handled in the next switch statement below.
break;
case INTERNAL_EXEC:
// We should have handled exec up above.
DIE("INTERNAL_EXEC process found in pipeline, where it should never be. Aborting.");
break;
}
if (exec_error) {
break;
}
switch (p->type) {
case INTERNAL_BLOCK_NODE:
case INTERNAL_FUNCTION: {
int status = proc_get_last_status();
// Handle output from a block or function. This usually means do nothing, but in the
// case of pipes, we have to buffer such io, since otherwise the internal pipe
// buffer might overflow.
if (!block_output_io_buffer.get()) {
// No buffer, so we exit directly. This means we have to manually set the exit
// status.
if (p->is_last_in_job) {
proc_set_last_status(j->get_flag(JOB_NEGATE) ? (!status) : status);
}
p->completed = 1;
break;
}
// Here we must have a non-NULL block_output_io_buffer.
assert(block_output_io_buffer.get() != NULL);
process_net_io_chain.remove(block_output_io_buffer);
block_output_io_buffer->read();
const char *buffer = block_output_io_buffer->out_buffer_ptr();
size_t count = block_output_io_buffer->out_buffer_size();
if (block_output_io_buffer->out_buffer_size() > 0) {
// We don't have to drain threads here because our child process is simple.
if (!do_fork(false, "internal block or function", [&] {
exec_write_and_exit(block_output_io_buffer->fd, buffer, count, status);
})) {
break;
}
} else {
if (p->is_last_in_job) {
proc_set_last_status(j->get_flag(JOB_NEGATE) ? (!status) : status);
}
p->completed = 1;
}
block_output_io_buffer.reset();
break;
}
case INTERNAL_BUILTIN: {
// Handle output from builtin commands. In the general case, this means forking of a
// worker process, that will write out the contents of the stdout and stderr buffers
// to the correct file descriptor. Since forking is expensive, fish tries to avoid
// it when possible.
bool fork_was_skipped = false;
const shared_ptr<io_data_t> stdout_io =
process_net_io_chain.get_io_for_fd(STDOUT_FILENO);
const shared_ptr<io_data_t> stderr_io =
process_net_io_chain.get_io_for_fd(STDERR_FILENO);
assert(builtin_io_streams.get() != NULL);
const wcstring &stdout_buffer = builtin_io_streams->out.buffer();
const wcstring &stderr_buffer = builtin_io_streams->err.buffer();
// If we are outputting to a file, we have to actually do it, even if we have no
// output, so that we can truncate the file. Does not apply to /dev/null.
bool must_fork = redirection_is_to_real_file(stdout_io.get()) ||
redirection_is_to_real_file(stderr_io.get());
if (!must_fork && p->is_last_in_job) {
// We are handling reads directly in the main loop. Make sure source is
// unblocked. Note that we may still end up forking.
unblock_previous();
const bool stdout_is_to_buffer = stdout_io && stdout_io->io_mode == IO_BUFFER;
const bool no_stdout_output = stdout_buffer.empty();
const bool no_stderr_output = stderr_buffer.empty();
const bool stdout_discarded = builtin_io_streams->out.output_discarded();
if (!stdout_discarded && no_stdout_output && no_stderr_output) {
// The builtin produced no output and is not inside of a pipeline. No
// need to fork or even output anything.
debug(3, L"Skipping fork: no output for internal builtin '%ls'",
p->argv0());
fork_was_skipped = true;
} else if (no_stderr_output && stdout_is_to_buffer) {
// The builtin produced no stderr, and its stdout is going to an
// internal buffer. There is no need to fork. This helps out the
// performance quite a bit in complex completion code.
debug(3, L"Skipping fork: buffered output for internal builtin '%ls'",
p->argv0());
io_buffer_t *io_buffer = static_cast<io_buffer_t *>(stdout_io.get());
if (stdout_discarded) {
io_buffer->set_discard();
} else {
const std::string res = wcs2string(builtin_io_streams->out.buffer());
io_buffer->out_buffer_append(res.data(), res.size());
}
fork_was_skipped = true;
} else if (stdout_io.get() == NULL && stderr_io.get() == NULL) {
// We are writing to normal stdout and stderr. Just do it - no need to fork.
debug(3, L"Skipping fork: ordinary output for internal builtin '%ls'",
p->argv0());
const std::string outbuff = wcs2string(stdout_buffer);
const std::string errbuff = wcs2string(stderr_buffer);
bool builtin_io_done = do_builtin_io(outbuff.data(), outbuff.size(),
errbuff.data(), errbuff.size());
if (!builtin_io_done && errno != EPIPE) {
redirect_tty_output(); // workaround glibc bug
debug(0, "!builtin_io_done and errno != EPIPE");
show_stackframe(L'E');
}
if (stdout_discarded) p->status = STATUS_READ_TOO_MUCH;
fork_was_skipped = true;
}
}
if (fork_was_skipped) {
p->completed = 1;
if (p->is_last_in_job) {
debug(3, L"Set status of %ls to %d using short circuit", j->command_wcstr(),
p->status);
int status = p->status;
proc_set_last_status(j->get_flag(JOB_NEGATE) ? (!status) : status);
}
} else {
// Ok, unfortunately, we have to do a real fork. Bummer. We work hard to make
// sure we don't have to wait for all our threads to exit, by arranging things
// so that we don't have to allocate memory or do anything except system calls
// in the child.
//
// These strings may contain embedded nulls, so don't treat them as C strings.
const std::string outbuff_str = wcs2string(stdout_buffer);
const char *outbuff = outbuff_str.data();
size_t outbuff_len = outbuff_str.size();
const std::string errbuff_str = wcs2string(stderr_buffer);
const char *errbuff = errbuff_str.data();
size_t errbuff_len = errbuff_str.size();
fflush(stdout);
fflush(stderr);
if (!do_fork(false, "internal builtin", [&] {
do_builtin_io(outbuff, outbuff_len, errbuff, errbuff_len);
exit_without_destructors(p->status);
})) {
break;
}
}
break;
}
case EXTERNAL: {
// Get argv and envv before we fork.
null_terminated_array_t<char> argv_array;
convert_wide_array_to_narrow(p->get_argv_array(), &argv_array);
// Ensure that stdin is blocking before we hand it off (see issue #176). It's a
// little strange that we only do this with stdin and not with stdout or stderr.
// However in practice, setting or clearing O_NONBLOCK on stdin also sets it for the
// other two fds, presumably because they refer to the same underlying file
// (/dev/tty?).
make_fd_blocking(STDIN_FILENO);
const char *const *argv = argv_array.get();
const char *const *envv = env_export_arr();
std::string actual_cmd_str = wcs2string(p->actual_cmd);
const char *actual_cmd = actual_cmd_str.c_str();
const wchar_t *file = reader_current_filename();
#if FISH_USE_POSIX_SPAWN
// Prefer to use posix_spawn, since it's faster on some systems like OS X.
bool use_posix_spawn = g_use_posix_spawn && can_use_posix_spawn_for_job(j, p);
if (use_posix_spawn) {
g_fork_count++; // spawn counts as a fork+exec
// Create posix spawn attributes and actions.
posix_spawnattr_t attr = posix_spawnattr_t();
posix_spawn_file_actions_t actions = posix_spawn_file_actions_t();
bool made_it = fork_actions_make_spawn_properties(&attr, &actions, j, p,
process_net_io_chain);
if (made_it) {
// We successfully made the attributes and actions; actually call
// posix_spawn.
int spawn_ret = posix_spawn(&pid, actual_cmd, &actions, &attr,
const_cast<char *const *>(argv),
const_cast<char *const *>(envv));
// This usleep can be used to test for various race conditions
// (https://github.com/fish-shell/fish-shell/issues/360).
// usleep(10000);
if (spawn_ret != 0) {
safe_report_exec_error(spawn_ret, actual_cmd, argv, envv);
// Make sure our pid isn't set.
pid = 0;
}
// Clean up our actions.
posix_spawn_file_actions_destroy(&actions);
posix_spawnattr_destroy(&attr);
}
// A 0 pid means we failed to posix_spawn. Since we have no pid, we'll never get
// told when it's exited, so we have to mark the process as failed.
debug(2, L"Fork #%d, pid %d: spawn external command '%s' from '%ls'",
g_fork_count, pid, actual_cmd, file ? file : L"<no file>");
if (pid == 0) {
job_mark_process_as_failed(j, p);
exec_error = true;
} else {
child_spawned = true;
}
} else
#endif
{
if (!do_fork(false, "external command",
[&] { safe_launch_process(p, actual_cmd, argv, envv); })) {
break;
}
}
// This is the parent process. Store away information on the child, and possibly
// fice it control over the terminal.
p->pid = pid;
break;
}
case INTERNAL_EXEC: {
// We should have handled exec up above.
DIE("INTERNAL_EXEC process found in pipeline, where it should never be. Aborting.");
break;
}
}
bool child_blocked = block_child && child_forked;
if (child_blocked) {
// We have to wait to ensure the child has set their progress group and is in SIGSTOP
// state otherwise, we can later call SIGCONT before they call SIGSTOP and they'll be
// blocked indefinitely. The child is SIGSTOP'd and is guaranteed to have called
// child_set_group() at this point. but we only need to call set_child_group for the
// first process in the group. If needs_keepalive is set, this has already been called
// for the keepalive process.
int result;
int pid_status;
while ((result = waitpid(p->pid, &pid_status, WUNTRACED)) == -1 && errno == EINTR) {
// This could be a superfluous interrupt or Ctrl+C at the terminal In all cases, it
// is OK to retry since the forking code above is specifically designed to never,
// ever hang/block in a child process before the SIGSTOP call is reached.
; // do nothing
}
if (result == -1) {
exec_error = true;
debug(1, L"waitpid(%d) call in unblock_pid failed:!\n", p->pid);
wperror(L"waitpid");
break;
}
// We are not unblocking the child via SIGCONT just yet to give the next process a
// chance to open the pipes and join the process group. We only unblock the last process
// in the job chain because no one awaits it.
}
// Regardless of whether the child blocked or not: only once per job, and only once we've
// actually executed an external command.
if ((child_spawned || child_forked) && !pgrp_set) {
// This should be called after waitpid if child_forked and pipes_to_next_command it can
// be called at any time if child_spawned.
set_child_group(j, p->pid);
// we can't rely on p->is_first_in_job because a builtin may have been the first.
pgrp_set = true;
}
// If the command we ran _before_ this one was SIGSTOP'd to let this one catch up, unblock
// it now. this must be after the wait_pid on the process we just started, if any.
unblock_previous();
if (child_blocked) {
// Store the newly-blocked command's PID so that it can be SIGCONT'd once the next
// process in the chain is started. That may be in this job or in another job.
blocked_pid = p->pid;
}
// Close the pipe the current process uses to read from the previous process_t.
if (pipe_current_read >= 0) {
exec_close(pipe_current_read);
pipe_current_read = -1;
}
// Close the write end too, since the curent child subprocess already has a copy of it.
if (pipe_current_write >= 0) {
exec_close(pipe_current_write);
pipe_current_write = -1;
}
// Unblock the last process because there's no need for it to stay SIGSTOP'd for anything.
if (p->is_last_in_job) {
unblock_previous();
}
}
// Clean up any file descriptors we left open.
if (pipe_current_read >= 0) exec_close(pipe_current_read);
if (pipe_current_write >= 0) exec_close(pipe_current_write);
if (pipe_next_read >= 0) exec_close(pipe_next_read);
// The keepalive process is no longer needed, so we terminate it with extreme prejudice.
if (needs_keepalive) {
kill(keepalive.pid, SIGKILL);
}
debug(3, L"Job is constructed");
j->set_flag(JOB_CONSTRUCTED, true);
if (!j->get_flag(JOB_FOREGROUND)) {
proc_last_bg_pid = j->pgid;
}
if (!exec_error) {
job_continue(j, false);
} else {
// Mark the errored job as not in the foreground. I can't fully justify whether this is the
// right place, but it prevents sanity_lose from complaining.
j->set_flag(JOB_FOREGROUND, false);
}
}
static int exec_subshell_internal(const wcstring &cmd, wcstring_list_t *lst, bool apply_exit_status,
bool is_subcmd) {
ASSERT_IS_MAIN_THREAD();
bool prev_subshell = is_subshell;
const int prev_status = proc_get_last_status();
bool split_output = false;
const auto ifs = env_get(L"IFS");
if (!ifs.missing_or_empty()) {
split_output = true;
}
is_subshell = true;
int subcommand_status = -1; // assume the worst
// IO buffer creation may fail (e.g. if we have too many open files to make a pipe), so this may
// be null.
const shared_ptr<io_buffer_t> io_buffer(
io_buffer_t::create(STDOUT_FILENO, io_chain_t(), is_subcmd ? read_byte_limit : 0));
if (io_buffer.get() != NULL) {
parser_t &parser = parser_t::principal_parser();
if (parser.eval(cmd, io_chain_t(io_buffer), SUBST) == 0) {
subcommand_status = proc_get_last_status();
}
io_buffer->read();
}
if (io_buffer->output_discarded()) subcommand_status = STATUS_READ_TOO_MUCH;
// If the caller asked us to preserve the exit status, restore the old status. Otherwise set the
// status of the subcommand.
proc_set_last_status(apply_exit_status ? subcommand_status : prev_status);
is_subshell = prev_subshell;
if (lst == NULL || io_buffer.get() == NULL) {
return subcommand_status;
}
const char *begin = io_buffer->out_buffer_ptr();
const char *end = begin + io_buffer->out_buffer_size();
if (split_output) {
const char *cursor = begin;
while (cursor < end) {
// Look for the next separator.
const char *stop = (const char *)memchr(cursor, '\n', end - cursor);
const bool hit_separator = (stop != NULL);
if (!hit_separator) {
// If it's not found, just use the end.
stop = end;
}
// Stop now points at the first character we do not want to copy.
const wcstring wc = str2wcstring(cursor, stop - cursor);
lst->push_back(wc);
// If we hit a separator, skip over it; otherwise we're at the end.
cursor = stop + (hit_separator ? 1 : 0);
}
} else {
// We're not splitting output, but we still want to trim off a trailing newline.
if (end != begin && end[-1] == '\n') {
--end;
}
const wcstring wc = str2wcstring(begin, end - begin);
lst->push_back(wc);
}
return subcommand_status;
}
int exec_subshell(const wcstring &cmd, std::vector<wcstring> &outputs, bool apply_exit_status,
bool is_subcmd) {
ASSERT_IS_MAIN_THREAD();
return exec_subshell_internal(cmd, &outputs, apply_exit_status, is_subcmd);
}
int exec_subshell(const wcstring &cmd, bool apply_exit_status, bool is_subcmd) {
ASSERT_IS_MAIN_THREAD();
return exec_subshell_internal(cmd, NULL, apply_exit_status, is_subcmd);
}
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