BTW this would allocate more for empty symlinks,
but they're rare: https://lwn.net/Articles/551224/
cheers,
Pádraig
>From 6be031b4c9d6cb742a010dbe3fe38f77fe515fec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A1draig=20Brady?= <p...@draigbrady.com>
Date: Thu, 4 Jul 2019 11:50:16 +0100
Subject: [PATCH] areadlink-with-size: guess a lower bound with 0 size
* lib/areadlink-with-size.c (areadlink_with_size): The size
is usually taken from st_size, which can be zero, resulting
in inefficient operation as seen with:
$ strace -e readlink stat -c %N /proc/$$/cwd
readlink("/proc/9036/cwd", "/", 1) = 1
readlink("/proc/9036/cwd", "/h", 2) = 2
readlink("/proc/9036/cwd", "/hom", 4) = 4
readlink("/proc/9036/cwd", "/home/pa", 8) = 8
readlink("/proc/9036/cwd", "/home/padraig", 16) = 13
Instead let zero select an appropriate lower bound,
as was already done for sizes more than 8Ki.
We also change SYMLINK_MAX to 1023 so that the initial
allocation is a power of two.
---
ChangeLog | 10 ++++++++++
lib/areadlink-with-size.c | 7 ++++---
2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index ea2e86a..bbd91f0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2019-07-04 Pádraig Brady <p...@draigbrady.com>
+
+ areadlink-with-size: guess a lower bound with 0 size
+ * lib/areadlink-with-size.c (areadlink_with_size):
+ SIZE is usually taken from st_size, which can be zero.
+ Instead let zero select an appropriate lower bound,
+ as was already done for sizes more than 8Ki.
+ We also change SYMLINK_MAX to 1023 so that the initial
+ allocation is a power of two.
+
2019-07-03 Bruno Haible <br...@clisp.org>
mbrtowc: Fix invalid use of mbtowc() on MSVC.
diff --git a/lib/areadlink-with-size.c b/lib/areadlink-with-size.c
index eacad3f..2fbe51c 100644
--- a/lib/areadlink-with-size.c
+++ b/lib/areadlink-with-size.c
@@ -36,14 +36,15 @@
check, so it's OK to guess too small on hosts where there is no
arbitrary limit to symbolic link length. */
#ifndef SYMLINK_MAX
-# define SYMLINK_MAX 1024
+# define SYMLINK_MAX 1023
#endif
#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
/* Call readlink to get the symbolic link value of FILE.
SIZE is a hint as to how long the link is expected to be;
- typically it is taken from st_size. It need not be correct.
+ typically it is taken from st_size. It need not be correct,
+ and a value of 0 (or more than 8Ki) will select an appropriate lower bound.
Return a pointer to that NUL-terminated string in malloc'd storage.
If readlink fails, malloc fails, or if the link value is longer
than SSIZE_MAX, return NULL (caller may use errno to diagnose). */
@@ -61,7 +62,7 @@ areadlink_with_size (char const *file, size_t size)
: INITIAL_LIMIT_BOUND);
/* The initial buffer size for the link value. */
- size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
+ size_t buf_size = size && size < initial_limit ? size + 1 : initial_limit;
while (1)
{
--
2.9.3
