On 2023-04-12 We 12:38, Dagfinn Ilmari Mannsåker wrote:
Andrew Dunstan<and...@dunslane.net> writes:
On 2023-04-12 We 10:23, Dagfinn Ilmari Mannsåker wrote:
Andrew Dunstan<and...@dunslane.net> writes:
On 2023-04-12 We 01:48, Thomas Munro wrote:
On Wed, Apr 12, 2023 at 3:04 PM Thomas Munro<thomas.mu...@gmail.com> wrote:
On Wed, Apr 12, 2023 at 2:56 PM Christoph Berg<m...@debian.org> wrote:
I'm hitting a panic in t_004_io_direct. The build is running on
overlayfs on tmpfs/ext4 (upper/lower) which is probably a weird
combination but has worked well for building everything over the last
decade. On Debian unstable:
PANIC: could not open file "pg_wal/000000010000000000000001": Invalid argument
... I have a new idea: perhaps it is possible to try
to open a file with O_DIRECT from perl, and if it fails like that,
skip the test. Looking into that now.
I think I have that working OK. Any Perl hackers want to comment on
my use of IO::File (copied from examples on the internet that showed
how to use O_DIRECT)? I am not much of a perl hacker but according to
my package manager, IO/File.pm came with perl itself. And the Fcntl
eval trick that I copied from File::stat, and the perl-critic
suppression that requires?
I think you can probably replace a lot of the magic here by simply saying
if (Fcntl->can("O_DIRECT")) ...
Fcntl->can() is true for all constants that Fcntl knows about, whether
or not they are defined for your OS. `defined &O_DIRECT` is the simplest
check, see my other reply to Thomas.
My understanding was that Fcntl only exported constants known to the
OS. That's certainly what its docco suggests, e.g.:
By default your system's F_* and O_* constants (eg, F_DUPFD and
O_CREAT)
and the FD_CLOEXEC constant are exported into your namespace.
It's a bit more magical than that (this is Perl after all). They are
all exported (which implicitly creates stubs visible to `->can()`,
similarly to forward declarations like `sub O_FOO;`), but only the
defined ones (`#ifdef O_FOO` is true) are defined (`defined &O_FOO` is
true). The rest fall through to an AUTOLOAD¹ function that throws an
exception for undefined ones.
Here's an example (Fcntl knows O_RAW, but Linux does not define it):
$ perl -E '
use strict; use Fcntl;
say "can", main->can("O_RAW") ? "" : "not";
say defined &O_RAW ? "" : "not ", "defined";
say O_RAW;'
can
not defined
Your vendor has not defined Fcntl macro O_RAW, used at -e line 4
While O_DIRECT is defined:
$ perl -E '
use strict; use Fcntl;
say "can", main->can("O_DIRECT") ? "" : "not";
say defined &O_DIRECT ? "" : "not ", "defined";
say O_DIRECT;'
can
defined
16384
And O_FOO is unknown to Fcntl (the parens on `O_FOO()q are to make it
not a bareword, which would be a compile error under `use strict;` when
the sub doesn't exist at all):
$ perl -E '
use strict; use Fcntl;
say "can", main->can("O_FOO") ? "" : "not";
say defined &O_FOO ? "" : "not ", "defined";
say O_FOO();'
cannot
not defined
Undefined subroutine &main::O_FOO called at -e line 4.
*grumble* a bit too magical for my taste. Thanks for the correction.
cheers
andrew
--
Andrew Dunstan
EDB:https://www.enterprisedb.com