Hello, I'm writing a small program which changes working dir to a specific directory (using chdir()), and then opens, reads, and closes files in that directory, depending on user actions. Sometimes this directory is located on a mounted USB stick.
I'm looking for a simple way to detect, from within my program, if a user have removed the USB stick without first unmounting it. The simplest way, I thought, was to check errno for EIO or ENXIO (depending on whether an error occurs in fread() or fopen()). However, that does not seem to work, because if I call fopen() after the USB stick has been removed, the return value is NULL, and the errno code is ENOENT instead of ENXIO, which sort of makes sense (the file certainly is not there any more), but the cause of the error cannot be differentiated from a regular mis-spelling of the file name. So is there some reliable way of detecting whether the underlying storage device has gone away when a library/system call fails, even if the OS still regards the filesystem as being mounted? Can I, upon detecting errno==ENOENT after fopen(), use some other calls (for example ioctl(), getfsstat(), or statfs()) to determine whether the cause is a mis-spelled filename or removed USB stick? What is the recommended/preferred way? Can/should I perhaps do something before attempting the fopen(), to find out whether the USB stick is still attached? I prefer simple solutions using standard library/system calls, and would like to avoid attaching to some notification mechanism, and tailing the kernel log looking for USB detach messages is a clumsy last chance solution. Dave
