Valerie Aurora: > My question: How often do applications actually attempt fchown(), > fchmod(), or utimensat() on an O_RDONLY file descriptor? Would it > break a lot of applications if a union mount file returned EBADF or > EPERM in this case? Unfortunately I don't know how often it is. But I am afraid it will be insufficient even if you implement the error. Do you remember the sample case I've written before? For instance, fd1 = open(path, O_RDONLY); fd2 = open(path, O_RDWR); fchmod(fd2); fstat(fd1, &st); In this case, fchmod will not return the error because fd2 is opened for write and the file would be copied-up. And the next fstat for fd1 will return a bogus info since fd1 still refers the file on the lower layer. Regardless fchmod() is issued by the same process or different one, fstat() lies. This is the same scenario I wrote before essentially (Jul 2009). Also we should take care of the file-locking. The copyup by UnionMount will break fcntl(F_SETLK) easily in the same scenario. But I am not sure how many applications depend upon file lock and UnionMount copyup affect. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
