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| author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2021-03-10 12:26:32 -0300 |
|---|---|---|
| committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2021-07-08 14:08:14 -0300 |
| commit | 607449506f197cc9514408908f41f22537a47a8c (patch) | |
| tree | 9d4304b8a8a1ccdef78a305433d845bcd3e08ae6 /manual | |
| parent | 286286283e9bdc7ef894306e2dbcf4c115b97ba2 (diff) | |
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io: Add closefrom [BZ #10353]
The function closes all open file descriptors greater than or equal to
input argument. Negative values are clamped to 0, i.e, it will close
all file descriptors.
As indicated by the bug report, this is a common symbol provided by
different systems (Solaris, OpenBSD, NetBSD, FreeBSD) and, although
its has inherent issues with not taking in consideration internal libc
file descriptors (such as syslog), this is also a common feature used
in multiple projects [1][2][3][4][5].
The Linux fallback implementation iterates over /proc and close all
file descriptors sequentially. Although it was raised the questioning
whether getdents on /proc/self/fd might return disjointed entries
when file descriptor are closed; it does not seems the case on my
testing on multiple kernel (v4.18, v5.4, v5.9) and the same strategy
is used on different projects [1][2][3][5].
Also, the interface is set a fail-safe meaning that a failure in the
fallback results in a process abort.
Checked on x86_64-linux-gnu and i686-linux-gnu on kernel 5.11 and 4.15.
[1] https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/fd-util.c#L217
[2] https://github.com/lxc/lxc/blob/ddf4b77e11a4d08f09b7b9cd13e593f8c047edc5/src/lxc/start.c#L236
[3] https://github.com/python/cpython/blob/9e4f2f3a6b8ee995c365e86d976937c141d867f8/Modules/_posixsubprocess.c#L220
[4] https://github.com/rust-lang/rust/blob/5f47c0613ed4eb46fca3633c1297364c09e5e451/src/libstd/sys/unix/process2.rs#L303-L308
[5] https://github.com/openjdk/jdk/blob/master/src/java.base/unix/native/libjava/childproc.c#L82
Diffstat (limited to 'manual')
| -rw-r--r-- | manual/llio.texi | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/manual/llio.texi b/manual/llio.texi index e21a71fdd0..2c59f6badf 100644 --- a/manual/llio.texi +++ b/manual/llio.texi @@ -334,6 +334,16 @@ The kernel does not implement the required functionality. @end table @end deftypefun +@deftypefun void closefrom (int @var{lowfd}) +@standards{GNU, unistd.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}} + +The function @code{closefrom} closes all file descriptors larger than or equal +to @var{lowfd} then @var{lowfd}. This function is similar to calling +@code{close} for all open file descriptors not less than @var{lowfd}. + +Already closed file descriptors are ignored. +@end deftypefun @node I/O Primitives @section Input and Output Primitives |