Why should I use fileno(stderr) instead of STDERR_FILENO

[Dima Rybakov (Tlt)]

Dear pgsql hackers,

I found a mixture of fileno(stderr) and STDERR_FILENO in PostgreSQL source
code which in most cases mean the same. But I have found recently that
Microsoft's fileno() _fileno() can return -2 sometimes. After some
experiments I found that applications running as windows service have
problems with stderr. I.e. fileno(stderr) returns -2 (negative two) in
windows service mode. That causes some issues with the logging collector.
Meanwhile the value of STDERR_FILENO always equals 2 and does not depend on
application mode because it is a macro.

I wonder if there are hidden advantages of using fileno(stderr) ?? Should I
use  only "fileno(stderr)" or using STDERR_FILENO is acceptable too ?? Are
there cases when I should not use STDERR_FILENO  ??

Sincerely,
Dmitry


Additional references
1. BUG #18400
2.
https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/fileno?view=msvc-170
Quote: "If stdout or stderr is not associated with an output stream (for
example, in a Windows application without a console window), the file
descriptor returned is -2. ..."

how to read table options during smgropen()

[Dima Rybakov (Tlt)]

Dear pgsql hackers,

I am developing custom storage for pgsql tables. I am using md* functions
and smgrsw[] structure to switch between different magnetic disk
access methods.

I want to add some custom options while table created
psql# create table t(...) with (my_option='value');

And thus I want to set "reln->smgr_which" conditionally during smgropen().
If myoption='value' i would use another smgr_which

I am really stuck at this point.

smgr.c:
SMgrRelation
smgropen(RelFileNode rnode, BackendId backend){
...
  if ( HasOption(rnode, "my_option","value")){ //<< how to implement this
check ?
reln->smgr_which = 1; //new access method
  }else{
reln->smgr_which = 0; //old access method
  }
...
}


The question is --- can I read table options while the table is
identified by  "RelFileNode rnode" ??

The only available information is
typedef struct RelFileNode
{
  Oid spcNode; /* tablespace */
  Oid dbNode; /* database */
  Oid relNode; /* relation */
} RelFileNode;

But there are no table options available directly from this structure.
What is the best way to implement HasOption(rnode, "my_option","value")

Thank you in advance for any ideas.
Sincerely,
Dmitry R