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clone.2: Document CLONE_PIDFD 

Add an entry for CLONE_PIDFD. This flag is available starting
with kernel 5.2. If specified, a process file descriptor
("pidfd") referring to the child process will be returned in
the ptid argument.

Signed-off-by: Christian Brauner <christian@brauner.io>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Christian Brauner 2019-05-11 08:49:08 +02:00 committed by Michael Kerrisk
parent a2dd6388a7
commit 9f93898154
1 changed files with 51 additions and 0 deletions
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@ -539,6 +539,42 @@ The flag disappeared completely from the kernel sources in Linux 2.5.16.
Since then, the kernel silently ignores this bit if it is specified in
.IR flags .
.TP
.BR CLONE_PIDFD " (since Linux 5.2)"
If
.B CLONE_PIDFD
is set,
.BR clone ()
stores a process file descriptor ("pidfd") referring to the child process at
the location
.I ptid
in the parent's memory. Note, that the kernel verifies that the value for
.I ptid
is zero. If it is not an error will be returned. This ensures that
.I ptid
can potentially be used to specify additional options for
.B CLONE_PIDFD
in the future.
.IP
Since the
.I ptid
argument is used to return the pidfd,
.B CLONE_PIDFD
cannot be used with
.B CLONE_PARENT_SETTID.
.IP
It is currently not possible to use this flag together with
.B CLONE_THREAD.
This means that the process identified by the pidfd will always be a
thread-group leader.
.IP
For a while there was a
.B CLONE_DETACHED
flag. This flag is usually ignored when passed along with other flags.
However, when passed alongside
.B CLONE_PIDFD
an error will be returned. This ensures that this flag can be reused
for further pidfd features in the future.
.TP
.BR CLONE_PTRACE " (since Linux 2.2)"
If
.B CLONE_PTRACE
@ -1122,6 +1158,21 @@ For example, on aarch64,
.I child_stack
must be a multiple of 16.
.TP
.B EINVAL
.B CLONE_PIDFD
was specified together with
.B CLONE_DETACHED.
.TP
.B EINVAL
.B CLONE_PIDFD
was specified together with
.B CLONE_PARENT_SETTID.
.TP
.B EINVAL
.B CLONE_PIDFD
was specified together with
.B CLONE_THREAD.
.TP
.B ENOMEM
Cannot allocate sufficient memory to allocate a task structure for the
child, or to copy those parts of the caller's context that need to be