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Date: Thu, 31 Aug 2023 16:17:36 +0200
From: Fabian =?iso-8859-1?q?Gr=FCnbichler?= <f.gruenbichler@proxmox.com>
To: Maximiliano Sandoval <m.sandoval@proxmox.com>, pmg-devel@lists.proxmox.com
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Subject: Re: [pmg-devel] [PATCH pmg-api] utils: check if file changed before
reusing its hash
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On August 31, 2023 3:33 pm, Maximiliano Sandoval wrote:
> We cache the hash of this file, it makes sense to first check if the
> file changed via `stat` and recompute the hash if needed.
>=20
> Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
> ---
> src/PMG/Utils.pm | 28 ++++++++++++++++++++++++----
> 1 file changed, 24 insertions(+), 4 deletions(-)
>=20
> diff --git a/src/PMG/Utils.pm b/src/PMG/Utils.pm
> index c19b31f..f8e6b7c 100644
> --- a/src/PMG/Utils.pm
> +++ b/src/PMG/Utils.pm
> @@ -49,6 +49,8 @@ postgres_admin_cmd
> try_decode_utf8
> );
> =20
> +my $host_rsa_key_path =3D '/etc/ssh/ssh_host_rsa_key.pub';
> +
> my $valid_pmg_realms =3D ['pam', 'pmg', 'quarantine'];
> =20
> PVE::JSONSchema::register_standard_option('realm', {
> @@ -1353,14 +1355,32 @@ sub scan_journal_for_rbl_rejects {
> }
> =20
> my $hwaddress;
> +my $hwaddress_st =3D {};
> +
> +sub get_server_id {
> + my $sshkey =3D PVE::Tools::file_get_contents($host_rsa_key_path);
> + return uc(Digest::MD5::md5_hex($sshkey));
> +}
> =20
> sub get_hwaddress {
> + my $st =3D stat($host_rsa_key_path);
> =20
> - return $hwaddress if defined ($hwaddress);
> + if (! defined($hwaddress)) {
FWIW, this condition
> + $hwaddress_st->{mtime} =3D $st->mtime;
> + $hwaddress_st->{ino} =3D $st->ino;
> + $hwaddress_st->{dev} =3D $st->dev;
> + $hwaddress =3D get_server_id();
> + }
> +
> + if ($hwaddress_st->{mtime} !=3D $st->mtime
> + || $hwaddress_st->{ino} !=3D $st->ino
> + || $hwaddress_st->{dev} !=3D $st->dev) {
and this one can be combined, since the executed code is the same, and
as long as the check for $hwaddress comes first, the condition will
short-circuit on the first execution (filling both variables), and
subsequent executions will compare the stat metadata.
> + $hwaddress_st->{mtime} =3D $st->mtime;
> + $hwaddress_st->{ino} =3D $st->ino;
> + $hwaddress_st->{dev} =3D $st->dev;
> =20
> - my $fn =3D '/etc/ssh/ssh_host_rsa_key.pub';
> - my $sshkey =3D PVE::Tools::file_get_contents($fn);
> - $hwaddress =3D uc(Digest::MD5::md5_hex($sshkey));
> + $hwaddress =3D get_server_id();
this change would then not be needed anymore ;)
I am not sure how often we have this pattern, and whether it's worth to
have a generic "read_cached_file" helper? e.g., like this:
my $cached =3D {};
sub something {
..
my $raw =3D read_cached_file($path, $cached);
..
}
where both (the original copy of?) $raw and the stat metadata are stored
in $cached, with the user not needing to know about the implementation
details?
just food for thought, most such things go through pmxcfs (which has its
own caching) and INotify (same) anyway..
> + }
> =20
> return $hwaddress;
> }
> --=20
> 2.39.2
>=20
>=20
>=20
> _______________________________________________
> pmg-devel mailing list
> pmg-devel@lists.proxmox.com
> https://lists.proxmox.com/cgi-bin/mailman/listinfo/pmg-devel
>=20
>=20
>=20