This patch documents two additional flags recently introduced
for the attr.sched_flags field of sched_setattr().
Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Branden:
*roff escape sequences may sometimes look like C escapes, but that
is misleading. *roff is in part a macro language and that means
recursive expansion to arbitrary depths.
You can get away with "\\" in a context where no macro expansion
is taking place, but try to spell a literal backslash this way in
the argument to a macro and you will likely be unhappy with
results.
Try viewing the attached file with "man -l".
"\e" is the preferred and portable way to get a portable "escape
literal" going back to CSTR #54, the original Bell Labs troff
paper.
groff(7) discusses the issue:
\\ reduces to a single backslash; useful to delay its
interpretation as escape character in copy mode. For a
printable backslash, use \e, or even better \[rs], to be
independent from the current escape character.
As of groff 1.22.4, groff_man(7) does as well:
\e Widely used in man pages to represent a backslash output
glyph. It works reliably as long as the .ec request is
not used, which should never happen in man pages, and it
is slightly more portable than the more exact ‘\(rs’
(“reverse solidus”) escape sequence.
People not concerned with portability to extremely old troffs should
probably just use \(rs (or \[rs]), as it means "the backslash
glyph", not "the glyph corresponding to whatever the current escape
character is".
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Branden:
*roff systems will interpret the period in the unpatched
page as sentence-ending punctuation and put inter-sentence
spacing after it. (This might not be visible on
nroff/terminal devices, but it is more likely to be on
typesetter/PostScript/PDF output).
groff_man(7) in groff 1.22.4 attempts to throw man page
writers a bone here:
\& Zero‐width space. Append to an input line to prevent
an end‐of‐ sentence punctuation sequence from being
recognized as such, or insert at the beginning of an
input line to prevent a dot or apostrophe from being
interpreted as the beginning of a roff request.
Reported-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Reported-by: G. Branden Robinson <g.branden.robinson@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
1) Use single-font macros for a single argument.
2) Use quotation marks for arguments containing a space.
3) Use roman font for punctuation marks.
The output has only changes of the font for a punctuation mark.
Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
fanotify_init.2: add new flag FAN_REPORT_TID
fanotify.7: update description of member pid in
struct fanotify_event_metadata
Signed-off-by: nixiaoming <nixiaoming@huawei.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Monitor fanotify events on the entire filesystem.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
New event masks have been added to the fanotify API. Documentation to
support the use and behaviour of these new masks has been added
accordingly.
Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Note EEXIST error that occurs when requesting a watch on a path
which is already watched with IN_MASK_CREATE.
Note EINVAL error also occurs when requesting a watch specifying
both IN_MASK_CREATE and IN_MASK_ADD.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The glibc wrapper was added in glibc 2.29, release on 1 Feb 2019.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
mtk: checked also against examples in samples/bpf
in kernel source to confirm.
Signed-off-by: Oded Elisha <oded123456@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The current manpage reads to me as if the kernel will always pick
a free space close to the requested address, but that's not the
case:
mmap(0x600000000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x600000000000
mmap(0x600000000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x7f5042859000
You can also see this in the various implementations of
->get_unmapped_area() - if the specified address isn't available,
the kernel basically ignores the hint (apart from the 5level
paging hack).
Clarify how this works a bit.
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
All address families are now documented in address_families.7,
which is already present in SEE ALSO section. Also, the AF_ALG
note contains dead link to kernel HTML documentation.
Signed-off-by: Nikola Forró <nforro@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
It has its own man page, so it probably makes sense to mention
it here.
* man2/socket.2 (.SH DESCRIPTION): Add mention of AF_VSOCK back.
Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
* man2/socket.2 (.SH DESCRIPTION): Mention that the list of
address families is Linux-specific.
* man7/address_families.7 (.SH DESCRIPTION): Likewise.
Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
* man2/sigaction.2 (.SS Undocumented): Provide information about
relation between the second argument of sa_handler and
uc_mcontext field of the struct ucontext structure.
Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Some architectures do provide an 'l_sysid' declaration in
struct flock; however, it is not used anyway.
* man2/fcntl.2 (.SH NOTES): Note that l_sysid field is not used on
Linux even if present on some architectures.
Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Remove crufty sentence suggesting use of deprecated capsetp(3) and
capgetp(3); the manual page for those functions has long (at least
as far back as 2007) noted that they are deprecated.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
O_RSYNC is defined in <asm/fcntl.h> on HP PA-RISC, but is not
used anyway.
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Add a note regarding other implementations of whiteout inodes
and update filesystem support information.
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This information is already summarized in syscall(2), so there's
no need to repeat it in each page.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Some architectures (ab)use second return value register for additional
return value in some system calls. Let's describe this.
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
As reported by Nadav Har'El in
https://bugzilla.kernel.org/show_bug.cgi?id=197961
The write(2) manual page has this paragraph:
"On success, the number of bytes written is returned
(zero indicates nothing was written). It is not an error
if this number is smaller than the number of bytes
requested; this may happen for example because the disk
device was filled. See also NOTES."
I find a few problems with this paragraph:
1. It's not clear what "See also NOTES." refers to (does it
refer to anything?). What in the NOTES is relevant here?
2. The paragraph seems to suggest that write(2) of a
non-empty buffer may sometimes return even 0 in case of an
error like the device being filled. I think this is wrong
- if there was an error after already writing some number
of bytes, this non-zero number is returned. But if there's
an error before writing any bytes, -1 will be returned
(and the error reason in errno) - 0 will not be returned
unless the given count is 0 (that case is explained in the
following paragraph).
3. The paragraph doesn't explain what a user should do
after a short write (i.e., write(2) returning less than
count). How would the user know why there was an error, or
if there even was one? I think users should be told what
to do next because this information is part of how to use
this API correctly. I think users should be told to retry
the rest of the write (i.e., write(fd, buf+ret, count-ret)
and this will either succeed in writing some more data if
the error reason was solved, or the second write will
return -1 and the error reason in errno.
Reported-by: Nadav Har'El <nyh@math.technion.ac.il>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
ENOATTR is not a standard error code, but rather one that is
defined in 'libattr' as a synonym for ENODATA. The manual pages
should use the error code actually returned by the kernel APIs.
See also https://bugzilla.kernel.org/show_bug.cgi?id=201995
Reported-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
alpha use v0 e.g. $0 as the return value register both in
syscall ABI and C ABI.
see also
https://github.com/torvalds/linux/blob/master/arch/alpha/kernel/entry.S#L479
The normal Alpha C ABI use a0~a5 to pass arguments and use v0 as
the return value register. See here
https://www2.cs.arizona.edu/projects/alto/Doc/local/alpha.register.html
The syscall ABI use v0 as the trap number, a0~a5 to pass arguments
and use a3 as a indicator (bool type) whether has a error occurred.
We can also see the libc's syscall wrapper implements at
https://code.woboq.org/userspace/glibc/sysdeps/unix/sysv/linux/alpha/syscall.S.html
The v0 is the normal used as return register, and we can see the
return processing doesn't do anything about a0 which is the wrong
register of currently syscall(2) description.
p.s. I found this wrong description because I'm porting Go gc to
a new CPU architecture which is similar to Alpha, And I use the
wrong register at first, then I have inspect the kernel code and
objdump to ensure the right syscall ABI.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Back in 2014 (37bee118ad) the text
describing when multiplexing happens was changed in a confusing way.
This is an attempt to clarify things a bit.
Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Since 93e06c7a6453 ("mm: enable MADV_FREE for swapless system") we
handle MADV_FREE on a swapless system the same way as with the
swap available. Clarify that fact in the man page.
Reported-by: Niklas Hambüchen <mail@nh2.me>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Remove the old statement that PTRACE_O_TRACESYSGOOD may not work
on all architectures. As far as I can tell, all kernel code
properly tests PT_TRACESYSGOOD flag and sets the 7th bit in the
exit code passed to ptrace_notify().
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
To test the behavior documented by this patch, the following
demos employ the program shown at the foot of this commit message.
First, show that the pdeath signal is sent when the parent
terminates:
$ ./pdeath_signal 0 10 4
Parent (18595) about to sleep for 4 seconds
Child about to set PR_SET_PDEATHSIG
Child about to sleep
Parent (18595) terminating
*********** Child (18596) got signal; si_pid = 18595; si_uid = 1000
Parent PID is now 1403
$ Child about to exit
But the signal is not sent if the parent terminates before the
child uses PR_SET_PDEATHSIG:
$ ./pdeath_signal 2 10 0
Parent (18707) about to sleep for 0 seconds
Parent (18707) terminating
Child about to sleep 2 seconds before setting PR_SET_PDEATHSIG
$ Child about to set PR_SET_PDEATHSIG
Child about to sleep
Child about to exit
Demonstrate that the pdeath signal is sent on termination of each
ancestor subreaper process:
$ ./pdeath_signal 2 10 3 7 6 5
18786 marked itself as a subreaper
18786 subreaper about to sleep 7 seconds
18787 marked itself as a subreaper
18787 subreaper about to sleep 6 seconds
18788 marked itself as a subreaper
18788 subreaper about to sleep 5 seconds
Parent (18789) about to sleep for 3 seconds
Child about to sleep 2 seconds before setting PR_SET_PDEATHSIG
Child about to set PR_SET_PDEATHSIG
Child about to sleep
Parent (18789) terminating
*********** Child (18790) got signal; si_pid = 18789; si_uid = 1000
Parent PID is now 18788
18788 subreaper about to terminate
*********** Child (18790) got signal; si_pid = 18788; si_uid = 1000
Parent PID is now 18787
18787 subreaper about to terminate
*********** Child (18790) got signal; si_pid = 18787; si_uid = 1000
Parent PID is now 18786
18786 subreaper about to terminate
*********** Child (18790) got signal; si_pid = 18786; si_uid = 1000
Parent PID is now 1403
$ Child about to exit
But in the case where some subreapers terminate before they
have a chance to adopt the child, the terminations of those
subreapers do not result in a signal for the child:
$ ./pdeath_signal 2 10 3 5 6 7
18836 marked itself as a subreaper
18836 subreaper about to sleep 5 seconds
18837 marked itself as a subreaper
18837 subreaper about to sleep 6 seconds
18838 marked itself as a subreaper
18838 subreaper about to sleep 7 seconds
Parent (18839) about to sleep for 3 seconds
Child about to sleep 2 seconds before setting PR_SET_PDEATHSIG
Child about to set PR_SET_PDEATHSIG
Child about to sleep
Parent (18839) terminating
*********** Child (18840) got signal; si_pid = 18839; si_uid = 1000
Parent PID is now 18838
18836 subreaper about to terminate
$ 18837 subreaper about to terminate
18838 subreaper about to terminate
*********** Child (18840) got signal; si_pid = 18838; si_uid = 1000
Parent PID is now 1403
Child about to exit
============================
/* pdeath_signal.c */
} while (0)
static void
handler(int sig, siginfo_t *si, void *ucontext)
{
printf("*********** Child (%ld) got signal; si_pid = %d; si_uid = %d\n",
(long) getpid(), si->si_pid, si->si_uid);
printf(" Parent PID is now %ld\n", (long) getppid());
}
int
main(int argc, char *argv[])
{
struct sigaction sa;
int childPreSleep, childPostSleep, parentSleep;
if (argc < 2) {
fprintf(stderr, "Usage: %s child-pre-sleep "
"[child-post-sleep [parent-sleep [subreaper-sleep...]]]\n",
argv[0]);
exit(EXIT_FAILURE);
}
childPreSleep = atoi(argv[1]);
if (argc > 2)
childPostSleep = atoi(argv[2]);
if (argc > 3)
parentSleep = atoi(argv[3]);
/* Optionally create a series of subreapers */
if (argc > 4) {
for (int sr = 4; sr < argc; sr++) {
if (prctl(PR_SET_CHILD_SUBREAPER, 1) == -1)
errExit("prctl");
printf("%ld marked itself as a subreaper\n", (long) getpid());
switch (fork()) {
case -1:
errExit("fork");
case 0:
break;
default:
printf("%ld subreaper about to sleep %s seconds\n",
(long) getpid(), argv[sr]);
sleep(atoi(argv[sr]));
printf("%ld subreaper about to terminate\n", (long) getpid());
exit(EXIT_SUCCESS);
}
}
}
switch (fork()) {
case -1:
errExit("fork");
case 0:
sa.sa_flags = SA_SIGINFO;
sigemptyset(&sa.sa_mask);
sa.sa_sigaction = handler;
if (sigaction(SIGUSR1, &sa, NULL) == -1)
errExit("sigaction");
if (childPreSleep > 0) {
printf("Child about to sleep %d seconds before setting "
"PR_SET_PDEATHSIG\n", childPreSleep);
sleep(childPreSleep);
}
printf("Child about to set PR_SET_PDEATHSIG\n");
if (prctl(PR_SET_PDEATHSIG, SIGUSR1) == -1)
errExit("prctl");
printf("Child about to sleep\n");
for (int j = 0; j < childPostSleep; j++)
sleep(1);
printf("Child about to exit\n");
exit(EXIT_SUCCESS);
default:
printf("Parent (%ld) about to sleep for %d seconds\n",
(long) getpid(), parentSleep);
sleep(parentSleep);
printf("Parent (%ld) terminating\n", (long) getpid());
exit(EXIT_SUCCESS);
}
}
Reported-by: Jann Horn <jann@thejh.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The signal is process directed and the siginfo_t->si_pid
filed contains the PID of the terminating parent.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
ptrace() with requests PTRACE_PEEKTEXT, PTRACE_PEEKDATA and
PTRACE_PEEKUSER can set errno to zero. AFAICS this is for a good
reason (so that you can tell the difference between a successful
PEEK with a result of -1 and a failed PEEK, even if you forget to
clear errno yourself), but it technically violates the rules
described in the errno.3 manpage.
glibc snippet from sysdeps/unix/sysv/linux/ptrace.c:
res = INLINE_SYSCALL (ptrace, 4, request, pid, addr, data);
if (res >= 0 && request > 0 && request < 4)
{
__set_errno (0);
return ret;
}
reproducer:
$ cat ptrace_test.c
char foobar_data[4] = "ABCD";
int main(void) {
pid_t child = fork();
if (child == -1) err(1, "fork");
if (child == 0) {
if (prctl(PR_SET_PDEATHSIG, SIGKILL)) err(1, "prctl");
while (1) sleep(1);
}
int status;
if (ptrace(PTRACE_ATTACH, child, NULL, NULL)) err(1, "attach");
if (waitpid(child, &status, 0) != child) err(1, "wait");
errno = EINVAL;
unsigned int res = ptrace(PTRACE_PEEKDATA, child, foobar_data, NULL);
printf("errno after PEEKDATA: %d\n", errno);
printf("PEEKDATA result: 0x%x\n", res);
}
$ gcc -o ptrace_test ptrace_test.c -Wall
$ ./ptrace_test
errno after PEEKDATA: 0
PEEKDATA result: 0x44434241
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk