In many cases I have seen an fstat call performed directly after the file descriptor has been assigned from a call to open:
fd = open(file, flags, mode);
fstat_result = fstat(fd, &stat_log);
Does fstat behave any differently if one has already performed a call to read first?
fd = open(file, flags, mode);
read_result = read(fd, buffer, buffersize)
fstat_result = fstat(fd, &stat_log);
And by "behave differently" I mean: Is the return value of fstat, or anything in the "struct stat" buffer output different in that scenario?
Do any of the size related members of stat_log now represent the size of the file remaining to be read?
If I have already read to the end of the file, will performing a call to fstat thereafter result in a failure? (fstat returning -1)
This fstat document doesn't seem to indicate any need for the file descriptor to reference a file that has not been read from yet. Have you found anything to indicate otherwise?
You can read from a file after opening it but before an fstat. The only thing that will change is any of the attributes that change as a result of that read. The only candidate would be atime, which would be the time of the read, which might be later than the time of the open.