Since adding checking to Android's bionic for file descriptor double-closes, we've found that the most common cause of these bugs is incorrect use of fileno(3). There appears to be a common misconception that it transfers ownership of the file descriptor to the caller. --- man3/ferror.3 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/man3/ferror.3 b/man3/ferror.3 index b45eb5559..609e10cf8 100644 --- a/man3/ferror.3 +++ b/man3/ferror.3 @@ -89,7 +89,15 @@ The function .BR fileno () examines the argument .I stream -and returns its integer file descriptor. +and returns the integer file descriptor used to implement this stream. +The file descriptor is still owned by +.I stream +and will be closed when +.BR fclose (3) +is called. +Duplicate the file descriptor with +.BR dup (2) +before passing it to code that might close it. .PP For nonlocking counterparts, see .BR unlocked_stdio (3). -- 2.19.0.605.g01d371f741-goog
From 7be1541bfbb9494614e2ecb7782918bf76548ff6 Mon Sep 17 00:00:00 2001 From: Elliott Hughes <enh@xxxxxxxxxx> Date: Mon, 1 Oct 2018 10:23:45 -0700 Subject: [PATCH] ferror.3: Warn about closing the result of fileno() Since adding checking to Android's bionic for file descriptor double-closes, we've found that the most common cause of these bugs is incorrect use of fileno(3). There appears to be a common misconception that it transfers ownership of the file descriptor to the caller. --- man3/ferror.3 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/man3/ferror.3 b/man3/ferror.3 index b45eb5559..609e10cf8 100644 --- a/man3/ferror.3 +++ b/man3/ferror.3 @@ -89,7 +89,15 @@ The function .BR fileno () examines the argument .I stream -and returns its integer file descriptor. +and returns the integer file descriptor used to implement this stream. +The file descriptor is still owned by +.I stream +and will be closed when +.BR fclose (3) +is called. +Duplicate the file descriptor with +.BR dup (2) +before passing it to code that might close it. .PP For nonlocking counterparts, see .BR unlocked_stdio (3). -- 2.19.0.605.g01d371f741-goog
