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job_t: use the sentinel value of -2 for new job process group IDs

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0 is not a good default PGID, because it's possible for a kernel process
to have the PGID of 0 under Linux.

This meant that job_get_from_pid could return incorrect jobs, as the PGID
for internal, non-forked jobs was the same as kernel processes.

Avoid this by using an invalid PGID as the initial PGID.
This commit is contained in:
David Adam 2017-04-23 22:56:33 +08:00
parent 16931f724b
commit f52708a20f
3 changed files with 14 additions and 5 deletions
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11
src/postfork.cpp
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@ -70,7 +70,8 @@ bool set_child_group(job_t *j, process_t *p, int print_errors) {
bool retval = true; bool retval = true;
if (j->get_flag(JOB_CONTROL)) { if (j->get_flag(JOB_CONTROL)) {
if (!j->pgid) { // New jobs have the pgid set to -2
if (j->pgid == -2) {
j->pgid = p->pid; j->pgid = p->pid;
} }
@ -322,10 +323,12 @@ bool fork_actions_make_spawn_properties(posix_spawnattr_t *attr,
if (j->get_flag(JOB_CONTROL)) { if (j->get_flag(JOB_CONTROL)) {
should_set_process_group_id = true; should_set_process_group_id = true;
// PCA: I'm quite fuzzy on process groups, but I believe that the default value of 0 means // set_child_group puts each job into its own process group
// that the process becomes its own group leader, which is what set_child_group did in this // do the same here if there is no PGID yet (i.e. PGID == -2)
// case. So we want this to be 0 if j->pgid is 0.
desired_process_group_id = j->pgid; desired_process_group_id = j->pgid;
if (desired_process_group_id == -2 ) {
desired_process_group_id = 0;
}
} }
// Set the handling for job control signals back to the default. // Set the handling for job control signals back to the default.

7
src/proc.cpp
View file

@ -362,8 +362,13 @@ process_t::process_t()
{ {
} }
/// The constructor sets the pgid to -2 as a sentinel value
/// 0 should not be used; although it is not a valid PGID in userspace,
/// the Linux kernel will use it for kernel processes.
/// -1 should not be used; it is a possible return value of the getpgid()
/// function
job_t::job_t(job_id_t jobid, const io_chain_t &bio) job_t::job_t(job_id_t jobid, const io_chain_t &bio)
: block_io(bio), pgid(0), tmodes(), job_id(jobid), flags(0) {} : block_io(bio), pgid(-2), tmodes(), job_id(jobid), flags(0) {}
job_t::~job_t() { release_job_id(job_id); } job_t::~job_t() { release_job_id(job_id); }

1
src/proc.h
View file

@ -217,6 +217,7 @@ class job_t {
process_list_t processes; process_list_t processes;
/// Process group ID for the process group that this job is running in. /// Process group ID for the process group that this job is running in.
/// Set to a nonexistent, non-return-value of getpgid() integer by the constructor
pid_t pgid; pid_t pgid;
/// The saved terminal modes of this job. This needs to be saved so that we can restore the /// The saved terminal modes of this job. This needs to be saved so that we can restore the
/// terminal to the same state after temporarily taking control over the terminal when a job /// terminal to the same state after temporarily taking control over the terminal when a job