[musl] fopen with "e" mode to close file descriptor in exec... functions

[musl] fopen with "e" mode to close file descriptor in exec... functions

[Alexander Scherbatiy]

[-- Attachment #1: Type: text/plain, Size: 1146 bytes --]

Hello,

Below is a simple program without any errors handling that uses
fopen with "ae" mode to open a "test.log" file with append access
and call posix_spawn to create a child process and list all open files for
the child process.

The program output shows that the child process has "test.log" file as open.
I used docker with Alpine Linux 3.11.3 (musl libc x86_64 1.1.24).
Is it an expected behaviour for Alpine Linux?

The same program on my Ubuntu 19.10 (with "ash" changed to "bash") shows
that
the child process doesn't have  "test.log" file as open.

Thanks,
Alexander.

----------  posix_spawn_sample.c ----------
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include <unistd.h>
#include <spawn.h>
#include <sys/wait.h>

extern char **environ;

int main()
{
    FILE* file = fopen("test.log", "ae");
    fprintf(file, "test line\n");

    pid_t pid;
    char *argv[] = {"bash", "-c", "echo PID=$$ && lsof -p $$", NULL};
    int status = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ);
    printf("Child pid: %i\n", pid);
    waitpid(pid, &status, 0);

    fclose(file);
    return 0;
}
--------------------------

[-- Attachment #2: Type: text/html, Size: 1691 bytes --]

Re: [musl] fopen with "e" mode to close file descriptor in exec... functions

[Rich Felker]

On Fri, Feb 07, 2020 at 09:22:01PM +0300, Alexander Scherbatiy wrote:
> Hello,
> 
> Below is a simple program without any errors handling that uses
> fopen with "ae" mode to open a "test.log" file with append access
> and call posix_spawn to create a child process and list all open files for
> the child process.
> 
> The program output shows that the child process has "test.log" file as open.
> I used docker with Alpine Linux 3.11.3 (musl libc x86_64 1.1.24).
> Is it an expected behaviour for Alpine Linux?
> 
> The same program on my Ubuntu 19.10 (with "ash" changed to "bash") shows
> that
> the child process doesn't have  "test.log" file as open.
> 
> Thanks,
> Alexander.
> 
> ----------  posix_spawn_sample.c ----------
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> 
> #include <unistd.h>
> #include <spawn.h>
> #include <sys/wait.h>
> 
> extern char **environ;
> 
> int main()
> {
>     FILE* file = fopen("test.log", "ae");
>     fprintf(file, "test line\n");
> 
>     pid_t pid;
>     char *argv[] = {"bash", "-c", "echo PID=$$ && lsof -p $$", NULL};
>     int status = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ);
>     printf("Child pid: %i\n", pid);
>     waitpid(pid, &status, 0);
> 
>     fclose(file);
>     return 0;
> }
> --------------------------

I can't reproduce this. I had to change /bin/sh to /bin/bash to be
able to run the test at all, and the lsof I have (busybox) doesn't
support -p, but I can't see any indication that the child has the log
file open. I also tried changing it to run "ls -l /proc/$$/fd" in the
child, and a fd 3 shows up there but prints an error because fd 3 is
the directory fd for listing /proc/$$/fd and it's closed before trying
to stat it -- apparently ash execs ls rather than running it as a
child. Indeed adding "; echo" makes that go away.

If you're still having the problem, could you attach a log of running
your test under "strace -f"?

Rich

Re: [musl] fopen with "e" mode to close file descriptor in exec... functions

[Alexander Scherbatiy]

[-- Attachment #1: Type: text/plain, Size: 13693 bytes --]

Below are steps to reproduce it in docker, logs from docker and strace log.

> docker run --rm -it alpine:3.11.3 ash
> apk add gcc
> apk add libc-dev
Copy the posix_spawn_sample.c code below (note it uses "ash" in 'char
*argv[] = {"ash", ,,,}' for posix_spawn on Alpine Linux )

> gcc -o posix_spawn_sample posix_spawn_sample.c
> ./posix_spawn_sample

--- output ---
/ # ./posix_spawn_sample
Child pid: 17
PID=17
1 /bin/busybox /dev/pts/0
1 /bin/busybox /dev/pts/0
1 /bin/busybox /dev/pts/0
1 /bin/busybox /dev/tty
16 /posix_spawn_sample /dev/pts/0
16 /posix_spawn_sample /dev/pts/0
16 /posix_spawn_sample /dev/pts/0
16 /posix_spawn_sample /test.log
----------------

Note that "test.log" file is listed by "lsof -p PID" command.

----------  posix_spawn_sample.c ----------
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include <unistd.h>
#include <spawn.h>
#include <sys/wait.h>

extern char **environ;

int main()
{
    FILE* file = fopen("test.log", "ae");
    fprintf(file, "test line\n");

    pid_t pid;
    // use "ash" for Alpine Linux and "bash" for Ubuntu
    char *argv[] = {"ash", "-c", "echo PID=$$ && lsof -p $$", NULL};
    int status = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ);
    printf("Child pid: %i\n", pid);
    waitpid(pid, &status, 0);

    fclose(file);
    return 0;
}
--------------------------

The full output step by step:
--------------------------------------
> docker run --rm -it alpine:3.11.3 ash
/ # apk add gcc
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/main/x86_64/APKINDEX.tar.gz
fetch
http://dl-cdn.alpinelinux.org/alpine/v3.11/community/x86_64/APKINDEX.tar.gz
(1/10) Installing libgcc (9.2.0-r3)
(2/10) Installing libstdc++ (9.2.0-r3)
(3/10) Installing binutils (2.33.1-r0)
(4/10) Installing gmp (6.1.2-r1)
(5/10) Installing isl (0.18-r0)
(6/10) Installing libgomp (9.2.0-r3)
(7/10) Installing libatomic (9.2.0-r3)
(8/10) Installing mpfr4 (4.0.2-r1)
(9/10) Installing mpc1 (1.1.0-r1)
(10/10) Installing gcc (9.2.0-r3)
Executing busybox-1.31.1-r9.trigger
OK: 101 MiB in 24 packages
/ # apk add libc-dev
(1/2) Installing musl-dev (1.1.24-r0)
(2/2) Installing libc-dev (0.7.2-r0)
OK: 111 MiB in 26 packages
/ #  gcc -o posix_spawn_sample posix_spawn_sample.c
/ # ./posix_spawn_sample
Child pid: 17
PID=17
1 /bin/busybox /dev/pts/0
1 /bin/busybox /dev/pts/0
1 /bin/busybox /dev/pts/0
1 /bin/busybox /dev/tty
16 /posix_spawn_sample /dev/pts/0
16 /posix_spawn_sample /dev/pts/0
16 /posix_spawn_sample /dev/pts/0
16 /posix_spawn_sample /test.log
--------------------------------------

strace log
--------------------------------------
/ # strace -f ./posix_spawn_sample
execve("./posix_spawn_sample", ["./posix_spawn_sample"], 0x7ffd951eb318 /*
6 vars */) = 0
arch_prctl(ARCH_SET_FS, 0x7f0fa33d6d48) = 0
set_tid_address(0x7f0fa33d731c)         = 31
mprotect(0x7f0fa33d3000, 4096, PROT_READ) = 0
mprotect(0x55e26cf7b000, 4096, PROT_READ) = 0
open("test.log", O_WRONLY|O_CREAT|O_APPEND|O_CLOEXEC, 0666) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fcntl(3, F_GETFL)                       = 0x8401 (flags
O_WRONLY|O_APPEND|O_LARGEFILE)
ioctl(3, TIOCGWINSZ, 0x7ffd87e838a8)    = -1 ENOTTY (Not a tty)
pipe2([4, 5], O_CLOEXEC)                = 0
rt_sigprocmask(SIG_BLOCK, ~[], [], 8)   = 0
clone(child_stack=0x7ffd87e838b8, flags=CLONE_VM|CLONE_VFORK|SIGCHLDstrace:
Process 32 attached
 <unfinished ...>
[pid    32] close(4)                    = 0
[pid    32] fcntl(5, F_SETFD, FD_CLOEXEC) = 0
[pid    32] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid    32] execve("/bin/sh", ["ash", "-c", "echo PID=$$ && lsof -p $$"],
0x7ffd87e83998 /* 6 vars */ <unfinished ...>
[pid    31] <... clone resumed>)        = 32
[pid    32] <... execve resumed>)       = 0
[pid    31] close(5 <unfinished ...>
[pid    32] arch_prctl(ARCH_SET_FS, 0x7f1a19d9ed48 <unfinished ...>
[pid    31] <... close resumed>)        = 0
[pid    31] read(4,  <unfinished ...>
[pid    32] <... arch_prctl resumed>)   = 0
[pid    31] <... read resumed>"", 4)    = 0
[pid    32] set_tid_address(0x7f1a19d9f31c <unfinished ...>
[pid    31] close(4 <unfinished ...>
[pid    32] <... set_tid_address resumed>) = 32
[pid    31] <... close resumed>)        = 0
[pid    32] mprotect(0x7f1a19d9b000, 4096, PROT_READ <unfinished ...>
[pid    31] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid    32] <... mprotect resumed>)     = 0
[pid    31] ioctl(1, TIOCGWINSZ, {ws_row=40, ws_col=155, ws_xpixel=0,
ws_ypixel=0}) = 0
[pid    32] mprotect(0x556eae13a000, 16384, PROT_READ <unfinished ...>
[pid    31] writev(1, [{iov_base="Child pid: 32", iov_len=13},
{iov_base="\n", iov_len=1}], 2 <unfinished ...>
[pid    32] <... mprotect resumed>)     = 0Child pid: 32

[pid    31] <... writev resumed>)       = 14
[pid    31] wait4(32,  <unfinished ...>
[pid    32] getuid()                    = 0
[pid    32] getpid()                    = 32
[pid    32] rt_sigprocmask(SIG_UNBLOCK, [RT_1 RT_2], NULL, 8) = 0
[pid    32] rt_sigaction(SIGCHLD, {sa_handler=0x556eae0b9dfc,
sa_mask=~[RTMIN RT_1 RT_2], sa_flags=SA_RESTORER,
sa_restorer=0x7f1a19d500d4}, NULL, 8) = 0
[pid    32] rt_sigaction(SIGHUP, {sa_handler=SIG_DFL, sa_mask=[],
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f1a19d500d4},
{sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
[pid    32] getppid()                   = 31
[pid    32] stat("/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
[pid    32] stat(".", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
[pid    32] rt_sigaction(SIGINT, NULL, {sa_handler=SIG_DFL, sa_mask=[],
sa_flags=0}, 8) = 0
[pid    32] rt_sigaction(SIGINT, {sa_handler=0x556eae0b9dfc,
sa_mask=~[RTMIN RT_1 RT_2], sa_flags=SA_RESTORER,
sa_restorer=0x7f1a19d500d4}, NULL, 8) = 0
[pid    32] rt_sigaction(SIGQUIT, NULL, {sa_handler=SIG_DFL, sa_mask=[],
sa_flags=0}, 8) = 0
[pid    32] rt_sigaction(SIGQUIT, {sa_handler=SIG_IGN, sa_mask=~[RTMIN RT_1
RT_2], sa_flags=SA_RESTORER, sa_restorer=0x7f1a19d500d4}, NULL, 8) = 0
[pid    32] rt_sigaction(SIGTERM, NULL, {sa_handler=SIG_DFL, sa_mask=[],
sa_flags=0}, 8) = 0
[pid    32] wait4(-1, 0x7fff4e3ea22c, WNOHANG, NULL) = -1 ECHILD (No child
process)
[pid    32] write(1, "PID=32\n", 7PID=32
)     = 7
[pid    32] stat("/usr/local/sbin/lsof", 0x7fff4e3ea170) = -1 ENOENT (No
such file or directory)
[pid    32] stat("/usr/local/bin/lsof", 0x7fff4e3ea170) = -1 ENOENT (No
such file or directory)
[pid    32] stat("/usr/sbin/lsof", 0x7fff4e3ea170) = -1 ENOENT (No such
file or directory)
[pid    32] stat("/usr/bin/lsof", {st_mode=S_IFREG|0755, st_size=841288,
...}) = 0
[pid    32] brk(NULL)                   = 0x556eaf7c5000
[pid    32] brk(0x556eaf7c6000)         = 0x556eaf7c6000
[pid    32] execve("/usr/bin/lsof", ["lsof", "-p", "32"], 0x556eae13ed80 /*
6 vars */) = 0
[pid    32] arch_prctl(ARCH_SET_FS, 0x7fe42bc41d48) = 0
[pid    32] set_tid_address(0x7fe42bc4231c) = 32
[pid    32] mprotect(0x7fe42bc3e000, 4096, PROT_READ) = 0
[pid    32] mprotect(0x55d56c79b000, 16384, PROT_READ) = 0
[pid    32] getuid()                    = 0
[pid    32] open("/proc", O_RDONLY|O_CLOEXEC|O_DIRECTORY) = 3
[pid    32] fcntl(3, F_SETFD, FD_CLOEXEC) = 0
[pid    32] getdents64(3, /* 67 entries */, 2048) = 1984
[pid    32] readlink("/proc/1/exe", "/bin/busybox", 80) = 12
[pid    32] getpid()                    = 32
[pid    32] open("/proc/1/fd/", O_RDONLY|O_CLOEXEC|O_DIRECTORY) = 4
[pid    32] fcntl(4, F_SETFD, FD_CLOEXEC) = 0
[pid    32] brk(NULL)                   = 0x55d56dac0000
[pid    32] brk(0x55d56dac1000)         = 0x55d56dac1000
[pid    32] getdents64(4, /* 6 entries */, 2048) = 144
[pid    32] readlink("/proc/1/fd/0", "/dev/pts/0", 80) = 10
[pid    32] ioctl(1, TIOCGWINSZ, {ws_row=40, ws_col=155, ws_xpixel=0,
ws_ypixel=0}) = 0
[pid    32] writev(1, [{iov_base="1\t/bin/busybox\t/dev/pts/0",
iov_len=25}, {iov_base="\n", iov_len=1}], 21 /bin/busybox /dev/pts/0
) = 26
[pid    32] readlink("/proc/1/fd/1", "/dev/pts/0", 80) = 10
[pid    32] writev(1, [{iov_base="1\t/bin/busybox\t/dev/pts/0",
iov_len=25}, {iov_base="\n", iov_len=1}], 21 /bin/busybox /dev/pts/0
) = 26
[pid    32] readlink("/proc/1/fd/2", "/dev/pts/0", 80) = 10
[pid    32] writev(1, [{iov_base="1\t/bin/busybox\t/dev/pts/0",
iov_len=25}, {iov_base="\n", iov_len=1}], 21 /bin/busybox /dev/pts/0
) = 26
[pid    32] readlink("/proc/1/fd/10", "/dev/tty", 80) = 8
[pid    32] writev(1, [{iov_base="1\t/bin/busybox\t/dev/tty", iov_len=23},
{iov_base="\n", iov_len=1}], 21 /bin/busybox /dev/tty
) = 24
[pid    32] getdents64(4, /* 0 entries */, 2048) = 0
[pid    32] close(4)                    = 0
[pid    32] readlink("/proc/28/exe", "/usr/bin/strace", 80) = 15
[pid    32] getpid()                    = 32
[pid    32] open("/proc/28/fd/", O_RDONLY|O_CLOEXEC|O_DIRECTORY) = 4
[pid    32] fcntl(4, F_SETFD, FD_CLOEXEC) = 0
[pid    32] getdents64(4, /* 5 entries */, 2048) = 120
[pid    32] readlink("/proc/28/fd/0", "pipe:[89317]", 80) = 12
[pid    32] writev(1, [{iov_base="28\t/usr/bin/strace\tpipe:[89317]",
iov_len=31}, {iov_base="\n", iov_len=1}], 228 /usr/bin/strace pipe:[89317]
) = 32
[pid    32] readlink("/proc/28/fd/1", "pipe:[89318]", 80) = 12
[pid    32] writev(1, [{iov_base="28\t/usr/bin/strace\tpipe:[89318]",
iov_len=31}, {iov_base="\n", iov_len=1}], 228 /usr/bin/strace pipe:[89318]
) = 32
[pid    32] readlink("/proc/28/fd/2", "/dev/pts/0", 80) = 10
[pid    32] writev(1, [{iov_base="28\t/usr/bin/strace\t/dev/pts/0",
iov_len=29}, {iov_base="\n", iov_len=1}], 228 /usr/bin/strace /dev/pts/0
) = 30
[pid    32] getdents64(4, /* 0 entries */, 2048) = 0
[pid    32] close(4)                    = 0
[pid    32] readlink("/proc/31/exe", "/posix_spawn_sample", 80) = 19
[pid    32] getpid()                    = 32
[pid    32] open("/proc/31/fd/", O_RDONLY|O_CLOEXEC|O_DIRECTORY) = 4
[pid    32] fcntl(4, F_SETFD, FD_CLOEXEC) = 0
[pid    32] getdents64(4, /* 6 entries */, 2048) = 144
[pid    32] readlink("/proc/31/fd/0", "/dev/pts/0", 80) = 10
[pid    32] writev(1, [{iov_base="31\t/posix_spawn_sample\t/dev/pts/"...,
iov_len=33}, {iov_base="\n", iov_len=1}], 231 /posix_spawn_sample /dev/pts/0
) = 34
[pid    32] readlink("/proc/31/fd/1", "/dev/pts/0", 80) = 10
[pid    32] writev(1, [{iov_base="31\t/posix_spawn_sample\t/dev/pts/"...,
iov_len=33}, {iov_base="\n", iov_len=1}], 231 /posix_spawn_sample /dev/pts/0
) = 34
[pid    32] readlink("/proc/31/fd/2", "/dev/pts/0", 80) = 10
[pid    32] writev(1, [{iov_base="31\t/posix_spawn_sample\t/dev/pts/"...,
iov_len=33}, {iov_base="\n", iov_len=1}], 231 /posix_spawn_sample /dev/pts/0
) = 34
[pid    32] readlink("/proc/31/fd/3", "/test.log", 80) = 9
[pid    32] writev(1, [{iov_base="31\t/posix_spawn_sample\t/test.log",
iov_len=32}, {iov_base="\n", iov_len=1}], 231 /posix_spawn_sample /test.log
) = 33
[pid    32] getdents64(4, /* 0 entries */, 2048) = 0
[pid    32] close(4)                    = 0
[pid    32] readlink("/proc/32/exe", "/bin/busybox", 80) = 12
[pid    32] getpid()                    = 32
[pid    32] getdents64(3, /* 0 entries */, 2048) = 0
[pid    32] close(3)                    = 0
[pid    32] exit_group(0)               = ?
[pid    32] +++ exited with 0 +++
<... wait4 resumed>[{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 32
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=32, si_uid=0,
si_status=0, si_utime=0, si_stime=0} ---
writev(3, [{iov_base="test line\n", iov_len=10}, {iov_base=NULL,
iov_len=0}], 2) = 10
close(3)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++
--------------------------------------

Thanks,
Alexander.


On Sat, Feb 8, 2020 at 12:03 AM Rich Felker <dalias@libc.org> wrote:

> On Fri, Feb 07, 2020 at 09:22:01PM +0300, Alexander Scherbatiy wrote:
> > Hello,
> >
> > Below is a simple program without any errors handling that uses
> > fopen with "ae" mode to open a "test.log" file with append access
> > and call posix_spawn to create a child process and list all open files
> for
> > the child process.
> >
> > The program output shows that the child process has "test.log" file as
> open.
> > I used docker with Alpine Linux 3.11.3 (musl libc x86_64 1.1.24).
> > Is it an expected behaviour for Alpine Linux?
> >
> > The same program on my Ubuntu 19.10 (with "ash" changed to "bash") shows
> > that
> > the child process doesn't have  "test.log" file as open.
> >
> > Thanks,
> > Alexander.
> >
> > ----------  posix_spawn_sample.c ----------
> > #include <stdlib.h>
> > #include <stdio.h>
> > #include <string.h>
> >
> > #include <unistd.h>
> > #include <spawn.h>
> > #include <sys/wait.h>
> >
> > extern char **environ;
> >
> > int main()
> > {
> >     FILE* file = fopen("test.log", "ae");
> >     fprintf(file, "test line\n");
> >
> >     pid_t pid;
> >     char *argv[] = {"bash", "-c", "echo PID=$$ && lsof -p $$", NULL};
> >     int status = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ);
> >     printf("Child pid: %i\n", pid);
> >     waitpid(pid, &status, 0);
> >
> >     fclose(file);
> >     return 0;
> > }
> > --------------------------
>
> I can't reproduce this. I had to change /bin/sh to /bin/bash to be
> able to run the test at all, and the lsof I have (busybox) doesn't
> support -p, but I can't see any indication that the child has the log
> file open. I also tried changing it to run "ls -l /proc/$$/fd" in the
> child, and a fd 3 shows up there but prints an error because fd 3 is
> the directory fd for listing /proc/$$/fd and it's closed before trying
> to stat it -- apparently ash execs ls rather than running it as a
> child. Indeed adding "; echo" makes that go away.
>
> If you're still having the problem, could you attach a log of running
> your test under "strace -f"?
>
> Rich
>

[-- Attachment #2: Type: text/html, Size: 17393 bytes --]

Re: [musl] fopen with "e" mode to close file descriptor in exec... functions

[Rich Felker]

On Sat, Feb 08, 2020 at 10:45:10AM +0300, Alexander Scherbatiy wrote:
> Below are steps to reproduce it in docker, logs from docker and strace log.
> 
> > docker run --rm -it alpine:3.11.3 ash
> > apk add gcc
> > apk add libc-dev
> Copy the posix_spawn_sample.c code below (note it uses "ash" in 'char
> *argv[] = {"ash", ,,,}' for posix_spawn on Alpine Linux )
> 
> > gcc -o posix_spawn_sample posix_spawn_sample.c
> > ./posix_spawn_sample
> 
> --- output ---
> / # ./posix_spawn_sample
> Child pid: 17
> PID=17
> 1 /bin/busybox /dev/pts/0
> 1 /bin/busybox /dev/pts/0
> 1 /bin/busybox /dev/pts/0
> 1 /bin/busybox /dev/tty
> 16 /posix_spawn_sample /dev/pts/0
> 16 /posix_spawn_sample /dev/pts/0
> 16 /posix_spawn_sample /dev/pts/0
> 16 /posix_spawn_sample /test.log
> ----------------
> 
> Note that "test.log" file is listed by "lsof -p PID" command.

It's listed as being owned by pid 16, the parent, not pid 17, the
child. That's expected. At first I didn't understand why lsof -p is
showing these additional pids (parent and init) in addition to the
requested one. But it seems since you're using Docker those are the
*only* pids running, and you just hit the issue that busybox lsof does
not support -p (or any options at all) and always lists all open files
for all processes.

It would be a lot better to have your test do like I suggested and ls
-l /proc/$$/fd rather than running lsof. Then you will very clearly
that the log file is not open. Or even run an interactive shell as the
child so you can explore /proc yourself from it.

Rich

Re: [musl] fopen with "e" mode to close file descriptor in exec... functions

[Alexander Scherbatiy]

Just a question about lsof options. On Ubuntu "lsof -q" gives: "lsof:
illegal option character: q".
Shouldn't busybox "lsof -p" give the similar error message?

Is there an open request to support "lsof -p" option in busybox?

Thanks,
Alexandr.

On 08.02.2020 19:19, Rich Felker wrote:
> On Sat, Feb 08, 2020 at 10:45:10AM +0300, Alexander Scherbatiy wrote:
>> Below are steps to reproduce it in docker, logs from docker and strace log.
>>
>>> docker run --rm -it alpine:3.11.3 ash
>>> apk add gcc
>>> apk add libc-dev
>> Copy the posix_spawn_sample.c code below (note it uses "ash" in 'char
>> *argv[] = {"ash", ,,,}' for posix_spawn on Alpine Linux )
>>
>>> gcc -o posix_spawn_sample posix_spawn_sample.c
>>> ./posix_spawn_sample
>> --- output ---
>> / # ./posix_spawn_sample
>> Child pid: 17
>> PID=17
>> 1 /bin/busybox /dev/pts/0
>> 1 /bin/busybox /dev/pts/0
>> 1 /bin/busybox /dev/pts/0
>> 1 /bin/busybox /dev/tty
>> 16 /posix_spawn_sample /dev/pts/0
>> 16 /posix_spawn_sample /dev/pts/0
>> 16 /posix_spawn_sample /dev/pts/0
>> 16 /posix_spawn_sample /test.log
>> ----------------
>>
>> Note that "test.log" file is listed by "lsof -p PID" command.
> It's listed as being owned by pid 16, the parent, not pid 17, the
> child. That's expected. At first I didn't understand why lsof -p is
> showing these additional pids (parent and init) in addition to the
> requested one. But it seems since you're using Docker those are the
> *only* pids running, and you just hit the issue that busybox lsof does
> not support -p (or any options at all) and always lists all open files
> for all processes.
>
> It would be a lot better to have your test do like I suggested and ls
> -l /proc/$$/fd rather than running lsof. Then you will very clearly
> that the log file is not open. Or even run an interactive shell as the
> child so you can explore /proc yourself from it.
>
> Rich

Re: [musl] fopen with "e" mode to close file descriptor in exec... functions

[Rich Felker]

On Mon, Feb 10, 2020 at 12:57:00PM +0300, Alexander Scherbatiy wrote:
> Just a question about lsof options. On Ubuntu "lsof -q" gives: "lsof:
> illegal option character: q".
> Shouldn't busybox "lsof -p" give the similar error message?
> 
> Is there an open request to support "lsof -p" option in busybox?

You could just install the full lsof with "apk add lsof". But there's
also a busybox bugtracker you could request it on. I think at least if
they're not going to support the options, busybox should error out on
them rather than ignoring them.

Rich


> On 08.02.2020 19:19, Rich Felker wrote:
> > On Sat, Feb 08, 2020 at 10:45:10AM +0300, Alexander Scherbatiy wrote:
> >> Below are steps to reproduce it in docker, logs from docker and strace log.
> >>
> >>> docker run --rm -it alpine:3.11.3 ash
> >>> apk add gcc
> >>> apk add libc-dev
> >> Copy the posix_spawn_sample.c code below (note it uses "ash" in 'char
> >> *argv[] = {"ash", ,,,}' for posix_spawn on Alpine Linux )
> >>
> >>> gcc -o posix_spawn_sample posix_spawn_sample.c
> >>> ./posix_spawn_sample
> >> --- output ---
> >> / # ./posix_spawn_sample
> >> Child pid: 17
> >> PID=17
> >> 1 /bin/busybox /dev/pts/0
> >> 1 /bin/busybox /dev/pts/0
> >> 1 /bin/busybox /dev/pts/0
> >> 1 /bin/busybox /dev/tty
> >> 16 /posix_spawn_sample /dev/pts/0
> >> 16 /posix_spawn_sample /dev/pts/0
> >> 16 /posix_spawn_sample /dev/pts/0
> >> 16 /posix_spawn_sample /test.log
> >> ----------------
> >>
> >> Note that "test.log" file is listed by "lsof -p PID" command.
> > It's listed as being owned by pid 16, the parent, not pid 17, the
> > child. That's expected. At first I didn't understand why lsof -p is
> > showing these additional pids (parent and init) in addition to the
> > requested one. But it seems since you're using Docker those are the
> > *only* pids running, and you just hit the issue that busybox lsof does
> > not support -p (or any options at all) and always lists all open files
> > for all processes.
> >
> > It would be a lot better to have your test do like I suggested and ls
> > -l /proc/$$/fd rather than running lsof. Then you will very clearly
> > that the log file is not open. Or even run an interactive shell as the
> > child so you can explore /proc yourself from it.
> >
> > Rich