[PATCH] make.conf.5: Sugest PORTAGE_LOG_FILTER_FILE_CMD supervisor for cat fallback (bug 781854)

If PORTAGE_LOG_FILTER_FILE_CMD fails after exec, then output
will be lost. Therefore, suggest to use bash as a supervisor,
with fallback to cat.

Bug: https://bugs.gentoo.org/781854
Signed-off-by: Zac Medico <[email protected]>
---
 man/make.conf.5 | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/man/make.conf.5 b/man/make.conf.5
index 8d551c95e..8a4a2ae30 100644
--- a/man/make.conf.5
+++ b/man/make.conf.5
@@ -1,4 +1,4 @@
-.TH "MAKE.CONF" "5" "Feb 2021" "Portage VERSION" "Portage"
+.TH "MAKE.CONF" "5" "Apr 2021" "Portage VERSION" "Portage"
 .SH "NAME"
 make.conf \- custom settings for Portage
 .SH "SYNOPSIS"
@@ -998,7 +998,18 @@ will set idle io priority. For more information about ionice, see
 .B PORTAGE_LOG_FILTER_FILE_CMD
 This variable specifies a command that filters build log output to a
 log file. In order to filter ANSI escape codes from build logs,
-\fBansifilter\fR(1) is a convenient setting for this variable.
+\fBansifilter\fR(1) is a convenient setting for this variable. Generally,
+PORTAGE_LOG_FILTER_FILE_CMD should include a supervisor that falls back
+to cat if the real filter command fails after exec. For example, a
+supervisor is needed for ansifilter, in case it fails after exec due to
+a problem resolving libstdc++ during a gcc upgrade.
+.br
+.I Example:
+.nf
+# Use bash as a supervisor, for fallback to cat if asifilter fails
+# after exec due to a problem resolving libstdc++ during a gcc upgrade.
+PORTAGE_LOG_FILTER_FILE_CMD="bash -c \\"ansifilter; exec cat\\""
+.fi
 .TP
 .B PORTAGE_LOGDIR
 This variable defines the directory in which per\-ebuild logs are kept.
-- 
2.26.2