check disk space before engaging TAPE record

[tehn]

make sure there is enough free disk space so the whole OS doesn't break.

[artfwo]

could be also implemented as auto-stopping recording when there's little or no space.

[catfact]

should add to new-crone Tape (auto-stop thread?)

statvfs f_bsize * f_bfree

#include <sys/statvfs.h>

       int statvfs(const char *path, struct statvfs *buf);
       int fstatvfs(int fd, struct statvfs *buf);

DESCRIPTION
       The function statvfs() returns information about a mounted file system.
       path is the pathname of any file within the mounted file  system.   buf
       is a pointer to a statvfs structure defined approximately as follows:

           struct statvfs {
               unsigned long  f_bsize;    /* file system block size */
               unsigned long  f_frsize;   /* fragment size */
               fsblkcnt_t     f_blocks;   /* size of fs in f_frsize units */
               fsblkcnt_t     f_bfree;    /* # free blocks */
               fsblkcnt_t     f_bavail;   /* # free blocks for unprivileged users */
               fsfilcnt_t     f_files;    /* # inodes */
               fsfilcnt_t     f_ffree;    /* # free inodes */
               fsfilcnt_t     f_favail;   /* # free inodes for unprivileged users */
               unsigned long  f_fsid;     /* file system ID */
               unsigned long  f_flag;     /* mount flags */
               unsigned long  f_namemax;  /* maximum filename length */
           };

[tehn]

i added a disk space checker to matron some time ago:

https://github.com/monome/norns/blob/master/matron/src/hardware/stat.c#L62

the logic is implemented in menu.lua for auto-stop