How do I find the size of mounted USB flash drive in C?

Question

I have a flash drive device (/dev/sda1) mounted to /mnt on an embedded linux system (kernel 2.6.23). Using C how do I work out the size of the drive?

Answer 1

On Linux, if you're not worried about portability (C doesn't know about drives, so any such specific code will be unportable), use statfs():

  struct statfs fsb;

  if(statfs("/mnt", &fsb) == 0)
    printf("device has %ld blocks, each %ld bytes\n", fsb.f_blocks, fsb.f_bsize);

Answer 2

Read and parse a number in device's sysfs entry. In your case,

1. Full device (all partitions and partition table): /sys/block/sda/size
2. Logical partition on this device: /sys/block/sda/sda1/size

The device does not have to be mounted yet.