https://bugzilla.kernel.org/show_bug.cgi?id=200043 Theodore Tso (tytso@xxxxxxx) changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |tytso@xxxxxxx --- Comment #3 from Theodore Tso (tytso@xxxxxxx) --- The answer is it depends on what version of the standard. Quoting from SuSv3: The POSIX.1-1990 standard did not specifically prohibit lseek() from returning a negative offset. Therefore, an application was required to clear errno prior to the call and check errno upon return to determine whether a return value of ( off_t)-1 is a negative offset or an indication of an error condition. The standard developers did not wish to require this action on the part of a conforming application, and chose to require that errno be set to [EINVAL] when the resulting file offset would be negative for a regular file, block special file, or directory. The main thing that the standards don't require that read(2)/lseek(2) on directories; the only thing is guaranteed to work is readdir()/telldir()/seekdir(). And the standards don't define fdopendir(), so there's no way to get access to the file descriptor associated with opendir(), and so there's no standard way to call lseek() on a directory stream. In actual practice, if you use fdopendir() and then try to use lseek(2) on it, the results will be chaos and readdir(2) will malfunction various wild and unpredictable ways. In any case, the problem seems to be in glibc; the system call lseek(2) returns 64-bit offsets. However, for backwards compatibility the lseek() function visible to userspace uses a 32-bit off_t type. And glibc() is not properly returning EOVERFLOW and is instead truncating the value returned by lseek. You can see this if you run strace on your test binary: lseek(3, -10, SEEK_END) = 9223372036854775797 write(1, "lseek returned: -11 (errno = 0)\n", 32lseek returned: -11 (errno = 0) ) = 32 lseek(3, -1, SEEK_END) = 9223372036854775806 write(1, "lseek returned: -2 (errno = 0)\n", 31lseek returned: -2 (errno = 0) ) = 31 In practice, it probably doesn't matter, because no sane program will be using lseek() in actual practice on a directory. It should be using opendir(2)/readdir(2)/telldir(2)/seekdir(3). And that all works correctly. -- You are receiving this mail because: You are watching the assignee of the bug.
