Full Disclosure mailing list archives
Re: Re: readdir_r considered harmful
From: Casper.Dik () Sun COM
Date: Sun, 06 Nov 2005 10:00:52 +0100
Then you never really understood the implementation, seems. Of course all implementations keep the content of the directory as read with getdents or so in the DIR descriptor. But it is usually not the case that the whole content fits into the buffer allocated. One could, of course, resize the buffer to fit the content of the directory read, even if this means reserving hundreds or thousands of kBs. But this is not how most implementations work.
I don't see how that is relevant; the typical use of readdir() is as follows: DIR *dirp = opendir(name); while ((dent = readdir(dirp)) != NULL) { ... } closedir(dirp); Nothing other threads do with readdir() on different dirp's will influence what "dent" points to. I have *never* seen a program where multiple threads read from a single dirp; and I can't image the use.
Instead implementations keep work similar to every buffered file I/O operation. But this means that buffer content is replaced. If this happens and some thread uses readdir() instead of readdir_r(), the returned string pointer suddenly becomes invalid since it points to memory which has been replaced.
Yes, the next call to readdir() *on the same dirp* may change what the previous call; but that's completely irrelevant for most uses of readdir(). Of course, an application may want to save all readdir() return values, but that is completely orthogonal to threads; there is no reason why the POSIX *thread* specification includes readdir_r().
Next time, before you make such comments, ask Don Cragun to explain things to you.
Next time before you mail, you might want to engage your brain. There is NO reason for a thread-safe library to use readdir_r() over readdir(), with common readdir() implementations. Casper _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/
Current thread:
- readdir_r considered harmful Ben Hutchings (Nov 01)
- Re: readdir_r considered harmful 3APA3A (Nov 01)
- Re: readdir_r considered harmful Ben Hutchings (Nov 01)
- Re: readdir_r considered harmful Ben Hutchings (Nov 01)
- Re: readdir_r considered harmful Casper . Dik (Nov 05)
- Re: Re: readdir_r considered harmful Ulrich Drepper (Nov 05)
- Re: Re: readdir_r considered harmful Casper . Dik (Nov 06)
- Re: Re: readdir_r considered harmful Ulrich Drepper (Nov 06)
- Re: Re: readdir_r considered harmful Casper . Dik (Nov 07)
- Re: Re: readdir_r considered harmful Andrew Miller (Nov 07)
- Re: Re: readdir_r considered harmful Ulrich Drepper (Nov 05)
- Re: Re: readdir_r considered harmful Andrew Farmer (Nov 07)
- Re: Re: readdir_r considered harmful Casper . Dik (Nov 08)
- Re: readdir_r considered harmful 3APA3A (Nov 01)