Re: [PATCH] strbuf: allocate enough space when strbuf_setlen() is called first time

Am 26.04.2011 17:32, schrieb Nguyen Thai Ngoc Duy:

2011/4/26 Junio C Hamano[off-list ref]:

quoted

Nguyễn Thái Ngọc Duy[off-list ref]  writes:

quoted

strbuf_grow(sb, 0) may allocate less than requested len and violate the
next assertion.

Signed-off-by: Nguyễn Thái Ngọc Duy<redacted>
---
  strbuf.h |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/strbuf.h b/strbuf.h
index 07060ce..ab213da 100644
--- a/strbuf.h
+++ b/strbuf.h

@@ -34,7 +34,7 @@ extern void strbuf_grow(struct strbuf *, size_t);

  static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
       if (!sb->alloc)
-             strbuf_grow(sb, 0);
+             strbuf_grow(sb, len);
       assert(len<  sb->alloc);

This looks so obviously correct that it is scary.

How could 60 callsites of this function manage to have run without crashes
so far?  They all happen to use the function on a buffer that already has
something on it?

I guess no current call site does _setlen right after initialization.
It's new code that triggers it.

Documentation/technical/api-strbuf.txt says that you can't use 
strbuf_setlen() to allocate more space for a strbuf, i.e. you can use it 
only to shorten a string or set it to its current length.  If the strbuf 
in question hasn't allocated any buffer at all (sb->alloc == 0) then the 
only valid len is zero.

Where is it used to extend strbufs, i.e. which is the new code you 
mentioned?

René