Greetings, Corinna Vinschen! > The problem here is about NAME_MAX. NAME_MAX is per POSIX[1] the > "maximum number of bytes in a filename (not including the terminating > null)."
Does this mean that POSIX standard is not compatible with real life? No surprise I was having hard times copying a rather simple directory structure to a UNIX servers. Just 2 levels deep with 4-5 words in each element name. > Note the word *bytes*. Not characters, bytes. UTF-8 chars are 1 to 4 > bytes in length. Thus, the maximum number of UTF-8 chars in a filename > is potentially less than NAME_MAX: > A filename of chars only from the basic latin charset (1 byte in UTF-8) > may consist of NAME_MAX characters, a filename solely constructed from > chars of the latin-1 supplement (2 byte chars) may consist of NAME_MAX / > 2 characters, a filename constructed from emoticons (4 byte chars) only > of NAME_MAX / 4 chars. > Ok, so we all know that Windows is not using a byte representation of > filenames, rather the OS uses UTF-16 to store and handle filenames > internally. Filename on Windows filesystems may consist of 255 UTF-16 > chars[2]. > How do you represent this in a byte-oriented POSIX system? What do you > set NAME_MAX to? You can't get it right due to the unfortunate multibyte > vs. UTF-16 encoding issue. > To cover all UTF-8 chars, NAME_MAX would have to be 1020. But then, > applications relying on NAME_MAX will be surprised by ENAMETOOLONG > errors for perfectly valid POSIX filenames. > If you make it 255, applications will be surprised by ENAMETOOLONG > errors for perfectly valid Windows filenames. > If you make it 255 on the application level but then return filenames > longer than 255 multibyte chars to the application, they will crash > due to buffer overflow issues. After all, NAME_MAX is a contractual > obligation. > There was also the backward compatibility issue. Back in the pre-Cygwin > 1.7 days, when Cygwin used the ANSI file API, NAME_MAX was already 255. > Changing that to a bigger value might have resulted in the > aforementioned application crashes due to buffer overflows as well. > So we decided to keep NAME_MAX at the same value as it always was, 255. > This restricts the actual filename length when using multibyte > characters just as on any other POSIX system with the downside that, > occasionally, a Windows filename will be too long to handle. > Sorry if that is frustrating in your current situation, but this > isn't something we can just change at a whim and go ahead. It would > break compatibility with all existing Cygwin executables. > Corinna > [1] http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html > [2] However, this does *not* cover NFS or other filesystems using a > byte representation for storing filenames. -- WBR, Andrey Repin (anrdae...@yandex.ru) 11.12.2013, <10:55> Sorry for my terrible english... -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
