>From b979980a653ce610fe5f64935adedda425da3ca4 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Sat, 6 Jul 2019 19:25:24 -0700 Subject: [PATCH] areadlink-with-size: avoid realloc when size==0 * lib/areadlink-with-size.c (areadlink_with_size): * lib/areadlinkat-with-size.c (areadlinkat_with_size): Reallocate at the end to the actual size, to avoid memory waste, as suggested by Bruno Haible. But when the guessed size is zero - useful when the size is unknown - do the initial small readlink into the stack, to avoid that realloc in the usual case. --- ChangeLog | 10 ++++++++++ lib/areadlink-with-size.c | 31 +++++++++++++++++++++++-------- lib/areadlinkat-with-size.c | 31 +++++++++++++++++++++++-------- 3 files changed, 56 insertions(+), 16 deletions(-) diff --git a/ChangeLog b/ChangeLog index 0b061317c..f7e031d9b 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,13 @@ +2019-07-06 Paul Eggert + + areadlink-with-size: avoid realloc when size==0 + * lib/areadlink-with-size.c (areadlink_with_size): + * lib/areadlinkat-with-size.c (areadlinkat_with_size): + Reallocate at the end to the actual size, to avoid memory waste, + as suggested by Bruno Haible. But when the guessed size is zero - + useful when the size is unknown - do the initial small readlink + into the stack, to avoid that realloc in the usual case. + 2019-07-06 Pádraig Brady areadlink-with-size: guess a buffer size with 0 size diff --git a/lib/areadlink-with-size.c b/lib/areadlink-with-size.c index b9cd05cba..ae3c782a4 100644 --- a/lib/areadlink-with-size.c +++ b/lib/areadlink-with-size.c @@ -60,19 +60,28 @@ areadlink_with_size (char const *file, size_t size) ? symlink_max + 1 : INITIAL_LIMIT_BOUND); + enum { stackbuf_size = 128 }; + /* The initial buffer size for the link value. */ - size_t buf_size = (size == 0 ? 128 + size_t buf_size = (size == 0 ? stackbuf_size : size < initial_limit ? size + 1 : initial_limit); while (1) { ssize_t r; size_t link_length; - char *buffer = malloc (buf_size); + char stackbuf[stackbuf_size]; + char *buf = stackbuf; + char *buffer = NULL; + + if (! (size == 0 && buf_size == stackbuf_size)) + { + buf = buffer = malloc (buf_size); + if (!buffer) + return NULL; + } - if (buffer == NULL) - return NULL; - r = readlink (file, buffer, buf_size); + r = readlink (file, buf, buf_size); link_length = r; /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 @@ -87,10 +96,16 @@ areadlink_with_size (char const *file, size_t size) if (link_length < buf_size) { - buffer[link_length] = 0; - /* Shrink BUFFER before returning it. */ - if (link_length + 1 < buf_size) + buf[link_length] = 0; + if (!buffer) + { + buffer = malloc (link_length + 1); + if (buffer) + return memcpy (buffer, buf, link_length + 1); + } + else if (link_length + 1 < buf_size) { + /* Shrink BUFFER before returning it. */ char *shrinked_buffer = realloc (buffer, link_length + 1); if (shrinked_buffer != NULL) buffer = shrinked_buffer; diff --git a/lib/areadlinkat-with-size.c b/lib/areadlinkat-with-size.c index d39096f2b..ed46d5911 100644 --- a/lib/areadlinkat-with-size.c +++ b/lib/areadlinkat-with-size.c @@ -65,19 +65,28 @@ areadlinkat_with_size (int fd, char const *file, size_t size) ? symlink_max + 1 : INITIAL_LIMIT_BOUND); + enum { stackbuf_size = 128 }; + /* The initial buffer size for the link value. */ - size_t buf_size = (size == 0 ? 128 + size_t buf_size = (size == 0 ? stackbuf_size : size < initial_limit ? size + 1 : initial_limit); while (1) { ssize_t r; size_t link_length; - char *buffer = malloc (buf_size); + char stackbuf[stackbuf_size]; + char *buf = stackbuf; + char *buffer = NULL; + + if (! (size == 0 && buf_size == stackbuf_size)) + { + buf = buffer = malloc (buf_size); + if (!buffer) + return NULL; + } - if (buffer == NULL) - return NULL; - r = readlinkat (fd, file, buffer, buf_size); + r = readlinkat (fd, file, buf, buf_size); link_length = r; /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 @@ -92,10 +101,16 @@ areadlinkat_with_size (int fd, char const *file, size_t size) if (link_length < buf_size) { - buffer[link_length] = 0; - /* Shrink BUFFER before returning it. */ - if (link_length + 1 < buf_size) + buf[link_length] = 0; + if (!buffer) + { + buffer = malloc (link_length + 1); + if (buffer) + return memcpy (buffer, buf, link_length + 1); + } + else if (link_length + 1 < buf_size) { + /* Shrink BUFFER before returning it. */ char *shrinked_buffer = realloc (buffer, link_length + 1); if (shrinked_buffer != NULL) buffer = shrinked_buffer; -- 2.17.1