Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 54)

CS485G Spring 2015 54

closedir(). readdir() returns a struct dirent pointer, which

includes the name of the ﬁle.

5. Directories associate ﬁle names with inode numbers, which uniquely

index the on-disk metadata for each ﬁle.

(a) Multiple directories can point to the same inode, in which case

a single ﬁle might have multiple path names.

(b) The on-disk inode includes a count of how many directories

point to it.

(d) To remove a name from a directory, use the unlink() system

call.

(e) When the last reference to a ﬁle is removed, the kernel can re-

claim the ﬁle’s allocated space on the disk.

6. Each open ﬁle includes a ﬁle position indicator for each open ﬁle; it

is advanced by read() and write() and a program can modify it

with lseek().

7. Lecture 30, 4/15/2015

8. Multiple processes may have the same ﬁle open.

(a) If they opened the ﬁle independently, each has its own ﬁle po-

sition.

(b) If they received the ﬁle descriptor by inheritance, they share the

ﬁle position.

9. The standard I/O library (#include <stdio.h>) provides buffered

versions of input and output.

(a) Instead of ﬁle descriptors (small integers), it uses pointers to a

FILE structure.

(b) It predeﬁnes stdin, stdout, stderr.

empty (input) or if there is an explicit request to fflush().

10. Choosing which calls to use in the program (low-level, stdio, or Rio):

(a) low-level: most general, lowest overhead per call, can access

ﬁle metadata, async-signal-safe (so they can be used in signal

handlers). But dealing with short counts is tricky, and I/O is

unbuffered, leading to multiple system calls.

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 66 67

Sin comentarios

Cirrus Logic CS485 Manual de usuario Pagina 54