The two main uses of dev_t are in struct stat and as a parameter of the mknod system calls. As of version 2.6.0 of the Linux kernel, dev_t is a 32-bit quantity with 12 bits set asaid for the major number and 20 for the minor number. The in-kernel dev_t encoded as MMMmmmmm, where M is a hex digit of the major number and m is a hex digit of the minor number. The user-space dev_t encoded as mmmM MMmm, where M and m is the major and minor numbers accordingly. This is downward compatible with legacy systems where dev_t is 16 bits wide, encoded as MMmm. In glibc dev_t is a 64-bit quantity, with 32-bit major and minor numbers, encoded as MMMM Mmmm mmmM MMmm. This is downward compatible with the Linux kernel and with legacy systems where dev_t is 16 bits wide. In the FreeBSD dev_t is a 64-bit quantity. The major and minor numbers are encoded as MMMmmmMm, therefore conversion of the device numbers between Linux user-space and FreeBSD kernel required. |
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