There's no evidence of physical disk traffic presented here (an efficient filesystem should do none for this short-lived-file, to which libpcp issues buffered I/O only), nor is there any evidence of "excess" syscalls being provided here.

If you intend to "fix" this (non-problem) please provide both a tested patch for more detailed discussion (this will help you realise its not going to be as trivial a change as you're thinking based on your initial reading of the code), some actual evidence of an actual observed problem being solved by it, and re-open.

(In reply to Nathan Scott from comment #1)
> There's no evidence of physical disk traffic presented here (an efficient
> filesystem should do none for this short-lived-file, to which libpcp issues
> buffered I/O only)

It does not take much thought to see why comment #0 true.  (Use of "buffered I/O" at the glibc level is irrelevant.)  The libpcp code is opening files on /var/tmp, which is normally a physical partition, not even a tmpfs.  It creates, writes-to, and closes the file.  Later it opens, reads, closes, and unlinks it.  A journaling filesystem can require physical & barriered I/O for several of these operations.


% cat foo.c
#include <pcp/pmapi.h>
int main ()
{ 
  for(;;) {
    pmprintf("hello");
    pmflush();
  }
}
% gcc foo.c -lpcp
% ./a.out 2>/dev/null

iostat shows at least journaling-related traffic; more if sync(1)'s are going in in the background.


> nor is there any evidence of "excess" syscalls being provided here.

Even one syscall is an excess over the apprx. zero needed for an in-memory buffering.  strace -t -t -T:

20:58:24.154035 open("/var/tmp/pcp-KzKLEM", O_RDWR|O_CREAT|O_EXCL, 0600) = 3 <0.
000023>
20:58:24.154067 umask(022)              = 0177 <0.000005>
20:58:24.154079 fcntl(3, F_GETFL)       = 0x8002 (flags O_RDWR|O_LARGEFILE) <0.0
00005>
20:58:24.154091 fcntl(3, F_SETFL, O_RDWR|O_APPEND|O_LARGEFILE) = 0 <0.000005>
20:58:24.154104 lseek(3, 0, SEEK_END)   = 0 <0.000005>
20:58:24.154128 fstat(3, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0 <0.000005>
20:58:24.154142 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2ab1c1db8000 <0.000006>
20:58:24.154158 write(3, "hello\n", 6)  = 6 <0.000009>
20:58:24.154175 lseek(3, 0, SEEK_SET)   = 0 <0.000005>
20:58:24.154187 read(3, "hello\n", 256) = 6 <0.000006>
20:58:24.154201 write(2, "hello\n", 6)  = 6 <0.000005>
20:58:24.154214 read(3, "", 256)        = 0 <0.000004>
20:58:24.154226 close(3)                = 0 <0.000006>
20:58:24.154239 munmap(0x2ab1c1db8000, 4096) = 0 <0.000007>
20:58:24.154254 unlink("/var/tmp/pcp-KzKLEM") = 0 <0.000013>
20:58:24.154277 umask(0177)             = 022 <0.000004>



> If you intend to "fix" this (non-problem) please provide both a tested patch

That is not a legitimate requirement for a bug report (or RFE).

OK, its all yours.  Those numbers so far don't suggest a real problem to me.

FWLIW, delayed allocation often means no disk traffic is actually required for short-lived files.  Buffered I/O is extremely important in this regard - if not used, then allocation & writing to disk is indeed unavoidable.

You will find the -file option to pmconfirm(1) complicates your proposed libpcp changes here, just as a heads-up.

This bug appears to have been reported against 'rawhide' during the Fedora 23 development cycle.
Changing version to '23'.

(As we did not run this process for some time, it could affect also pre-Fedora 23 development
cycle bugs. We are very sorry. It will help us with cleanup during Fedora 23 End Of Life. Thank you.)

More information and reason for this action is here:
https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora23

This message is a reminder that Fedora 23 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 23. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
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Although we aim to fix as many bugs as possible during every release's 
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more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

This bug appears to have been reported against 'rawhide' during the Fedora 26 development cycle.
Changing version to '26'.

kenj is kindly fixing this problem
https://github.com/kmcdonell/pcp/commit/cb92d3474c5fea8f6da6b47e43d7e238fcea55fe

This message is a reminder that Fedora 26 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 26. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '26'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version'
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not
able to fix it before Fedora 26 is end of life. If you would still like
to see this bug fixed and are able to reproduce it against a later version
of Fedora, you are encouraged  change the 'version' to a later Fedora
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's
lifetime, sometimes those efforts are overtaken by events. Often a
more recent Fedora release includes newer upstream software that fixes
bugs or makes them obsolete.

This bug appears to have been reported against 'rawhide' during the Fedora 29 development cycle.
Changing version to '29'.

fixed by commit cb92d3474c5fea8f6da6b47e43d7e238fcea55fe
Author: Ken McDonell <kenj.au>
Date:   Sun Feb 18 15:28:43 2018 +1100