Stat mmap and file Stat mmap and file system interfacesystem interfaceNezer J. ZaidenbergNezer J. Zaidenberg

Stat(2)Stat(2)

NAMENAME

stat, lstat, fstat -- get file statusstat, lstat, fstat -- get file status

SYNOPSISSYNOPSIS

#include <sys/types.h>#include <sys/types.h>

#include <sys/stat.h>#include <sys/stat.h>

int stat(const char *path, struct stat *sb);int stat(const char *path, struct stat *sb);

int lstat(const char *path, struct stat *sb);int lstat(const char *path, struct stat *sb);

int fstat(int fd, struct stat *sb);int fstat(int fd, struct stat *sb);

Struct stat (1/2))Struct stat (1/2))

struct stat {struct stat {

dev_t st_dev; /* device inode resides on */dev_t st_dev; /* device inode resides on */

ino_t st_ino; /* inode's number */ino_t st_ino; /* inode's number */

mode_t st_mode; /* inode protection mode */mode_t st_mode; /* inode protection mode */

nlink_t st_nlink; /* number or hard links to the file nlink_t st_nlink; /* number or hard links to the file */*/

uid_t st_uid; /* user-id of owner */uid_t st_uid; /* user-id of owner */

gid_t st_gid; /* group-id of owner */gid_t st_gid; /* group-id of owner */

dev_t st_rdev; /* device type, for special file dev_t st_rdev; /* device type, for special file inode */inode */

Struct stat (2/2)Struct stat (2/2)

struct timespec st_atimespec; /* time of last access */struct timespec st_atimespec; /* time of last access */

struct timespec st_mtimespec; /* time of last data modification */struct timespec st_mtimespec; /* time of last data modification */

struct timespec st_ctimespec; /* time of last file status change */struct timespec st_ctimespec; /* time of last file status change */

off_t st_size; /* file size, in bytes */off_t st_size; /* file size, in bytes */

quad_t st_blocks; /* blocks allocated for file */quad_t st_blocks; /* blocks allocated for file */

u_long st_blksize;/* optimal file sys I/O ops blocksize */u_long st_blksize;/* optimal file sys I/O ops blocksize */

u_long st_flags; /* user defined flags for file */u_long st_flags; /* user defined flags for file */

u_long st_gen; /* file generation number */u_long st_gen; /* file generation number */

};};

Unlink(2)Unlink(2)

NAMENAME

unlink -- remove directory entryunlink -- remove directory entry

SYNOPSISSYNOPSIS

#include <unistd.h>#include <unistd.h>

intint

unlink(const char *path);unlink(const char *path);

Lseek(2)Lseek(2)

NAMENAME

lseek -- reposition read/write file offsetlseek -- reposition read/write file offset

SYNOPSISSYNOPSIS

#include <unistd.h>#include <unistd.h>

off_toff_t

lseek(int fildes, off_t offset, int whence);lseek(int fildes, off_t offset, int whence);

Creat(2)Creat(2)

SYNOPSISSYNOPSIS

#include <fcntl.h>#include <fcntl.h>

intint

creat(const char *path, mode_t mode);creat(const char *path, mode_t mode);

Dup(2)Dup(2)

SYNOPSISSYNOPSIS

#include <unistd.h>#include <unistd.h>

intint

dup(int oldd);dup(int oldd);

intint

dup2(int oldd, int newd);dup2(int oldd, int newd);

Flock(2)Flock(2)

SYNOPSISSYNOPSIS

#include <sys/file.h>#include <sys/file.h>

#define LOCK_SH 1 /* shared lock */#define LOCK_SH 1 /* shared lock */

#define LOCK_EX 2 /* exclusive lock */#define LOCK_EX 2 /* exclusive lock */

#define LOCK_NB 4 /* don't block when locking */#define LOCK_NB 4 /* don't block when locking */

#define LOCK_UN 8 /* unlock */#define LOCK_UN 8 /* unlock */

intint

flock(int fd, int operation);flock(int fd, int operation);

Fcntl(2)Fcntl(2)

SYNOPSISSYNOPSIS

#include <fcntl.h>#include <fcntl.h>

intint

fcntl(int fd, int cmd, int arg);fcntl(int fd, int cmd, int arg);

LinkingLinking

Symlink(2)Symlink(2)

Link(2)Link(2)

Create soft and hard linkCreate soft and hard link

Memory mappingMemory mapping

Mmap(2)Mmap(2)

Munmap(2)Munmap(2)

Msync(2)Msync(2)

Mmap(2)Mmap(2)

Copy a file to memory Copy a file to memory

This memory can be shared (among process) or lockedThis memory can be shared (among process) or locked

Check mprotect(2) for locking option (beyond our Check mprotect(2) for locking option (beyond our scope)scope)

Use msync(2) to write changesUse msync(2) to write changes

Use munmap(2) to write and free memoryUse munmap(2) to write and free memory

Homework : use read(2) and write(2) to copy file. Then Homework : use read(2) and write(2) to copy file. Then use mmap and memory copy. What works faster?use mmap and memory copy. What works faster?

Mmap(2)Mmap(2)

NAMENAME

mmap -- map files or devices into memorymmap -- map files or devices into memory

SYNOPSISSYNOPSIS

#include <sys/mman.h>#include <sys/mman.h>

void *void *

mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t offset);offset);

Munmap(2)Munmap(2)

NAMENAME

munmap -- remove a mappingmunmap -- remove a mapping

SYNOPSISSYNOPSIS

#include <sys/mman.h>#include <sys/mman.h>

int munmap(void *addr, size_t len);int munmap(void *addr, size_t len);

Msync(2)Msync(2)

NAMENAME

msync -- synchronize a mapped regionmsync -- synchronize a mapped region

SYNOPSISSYNOPSIS

#include <sys/mman.h>#include <sys/mman.h>

int msync(void *addr, size_t len, int int msync(void *addr, size_t len, int flags);flags);

Example (1/2)Example (1/2)

#include <sys/types.h>#include <sys/types.h>

#include <sys/stat.h>#include <sys/stat.h>

#include <sys/mman.h> /* mmap() is defined in this header */#include <sys/mman.h> /* mmap() is defined in this header */

#include <fcntl.h>#include <fcntl.h>

int main (int argc, char *argv[]) // will be used as cp source destint main (int argc, char *argv[]) // will be used as cp source dest

{{

int fdin, fdout;int fdin, fdout;

char *src, *dst;char *src, *dst;

struct stat statbuf;struct stat statbuf;

fdin = open (argv[1], O_RDONLY);fdin = open (argv[1], O_RDONLY);

fdout = open (argv[2], O_RDWR | O_CREAT | O_TRUNC, FILE_MODE);fdout = open (argv[2], O_RDWR | O_CREAT | O_TRUNC, FILE_MODE);

Example 2/2Example 2/2

fstat (fdin,&statbuf); // get sizefstat (fdin,&statbuf); // get size

lseek (fdout, statbuf.st_size - 1, SEEK_SET); // go to the location lseek (fdout, statbuf.st_size - 1, SEEK_SET); // go to the location corresponding to the last bytecorresponding to the last byte

write (fdout, "", 1) // output file now the size of input filewrite (fdout, "", 1) // output file now the size of input file

/* mmap the input and output file *//* mmap the input and output file */

src = mmap (0, statbuf.st_size, PROT_READ, MAP_SHARED, fdin, 0);src = mmap (0, statbuf.st_size, PROT_READ, MAP_SHARED, fdin, 0);

dst = mmap (0, statbuf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, dst = mmap (0, statbuf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fdout, 0);fdout, 0);

memcpy (dst, src, statbuf.st_size);memcpy (dst, src, statbuf.st_size);

} // if we wanted to write and continue we had to use munmap or msync } // if we wanted to write and continue we had to use munmap or msync

SignalsSignalsDebt from homeworkDebt from homework

Signal(3)Signal(3)

SYNOPSISSYNOPSIS

#include <signal.h>#include <signal.h>

void (*void (*

signal(int sig, void (*func)(int)))(int);signal(int sig, void (*func)(int)))(int);

or in the equivalent but easier to read typedef'd or in the equivalent but easier to read typedef'd version:version:

typedef void (*sig_t) (int);typedef void (*sig_t) (int);

sig_tsig_t

signal(int sig, sig_t func);signal(int sig, sig_t func);

Sigaction(2) (1/2)Sigaction(2) (1/2)

SYNOPSISSYNOPSIS

#include <signal.h>#include <signal.h>

struct sigaction { union {struct sigaction { union {

void (*__sa_handler)(int);void (*__sa_handler)(int);

void (*__sa_sigaction)(int, struct __siginfo *, void *);void (*__sa_sigaction)(int, struct __siginfo *, void *);

} __sigaction_u; /* signal handler */} __sigaction_u; /* signal handler */

int sa_flags; /* see signal options below */int sa_flags; /* see signal options below */

sigset_t sa_mask; /* signal mask to apply */sigset_t sa_mask; /* signal mask to apply */

};};

Sigaction(2) 2/2Sigaction(2) 2/2

#define sa_handler #define sa_handler __sigaction_u.__sa_handler__sigaction_u.__sa_handler

#define sa_sigaction #define sa_sigaction __sigaction_u.__sa_sigaction__sigaction_u.__sa_sigaction

intint

sigaction(int sig, const struct sigaction * sigaction(int sig, const struct sigaction * restrict act,restrict act,

struct sigaction * restrict oact);struct sigaction * restrict oact);

Kill(2)Kill(2)

SYNOPSISSYNOPSIS

#include <signal.h>#include <signal.h>

intint

kill(pid_t pid, int sig);kill(pid_t pid, int sig);

What you may do in a What you may do in a sig handlersig handler

Signal handler are very low level code. They are Signal handler are very low level code. They are invoked by the kernel, as an interrupt to the invoked by the kernel, as an interrupt to the program (even while doing other system call) – program (even while doing other system call) – some of you got EINTR on select(2)some of you got EINTR on select(2)

Therefore we must not get another interrupt on Therefore we must not get another interrupt on signal handler. signal handler.

Use only memory operation and non blocking Use only memory operation and non blocking system calls. (specifically avoid file I/O on signal system calls. (specifically avoid file I/O on signal hanglers)hanglers)

Getting another signal on signal handler may result Getting another signal on signal handler may result in undefined behavior or even damned recursionin undefined behavior or even damned recursion

FAQFAQFrom homeworkFrom homework

debuggingdebugging

Gdb – lowest levelGdb – lowest level

Ddd – graphical front endDdd – graphical front end

Compile flag for debugging - -gCompile flag for debugging - -g

Create coredump Create coredump (tcsh) setenv coredumpsize 100000000(tcsh) setenv coredumpsize 100000000 (bash) ulimit –c 10000000000(bash) ulimit –c 10000000000

Traces: ptrace(1) strace(1)Traces: ptrace(1) strace(1)

Top : display list of process with CPU usageTop : display list of process with CPU usage

Kill -9 pid = kill one of your processesKill -9 pid = kill one of your processes

findfind

Grep = find in file (grep terlala *.h */*.h)Grep = find in file (grep terlala *.h */*.h)

/usr/include = where most of the include are/usr/include = where most of the include are

/usr/bin = where most exe are/usr/bin = where most exe are

Vi commands for Vi commands for programming (1/2)programming (1/2)

~/.vimrc = commands that run on each new vi ~/.vimrc = commands that run on each new vi sessionsession

<esc>:set nu = line numbers<esc>:set nu = line numbers

<esc>:set ai = auto ident<esc>:set ai = auto ident

<esc>:set ts=4 = tabstop=4<esc>:set ts=4 = tabstop=4

<esc>:set sw=4 = shiftwidth=4<esc>:set sw=4 = shiftwidth=4

>> << = ident one shift width inside or outside>> << = ident one shift width inside or outside

sy on = syntax enlightment on and offsy on = syntax enlightment on and off

Vi commands for Vi commands for programming 2/2programming 2/2

Name completion, jumping to function Name completion, jumping to function declaration /definition = man ctags(1)declaration /definition = man ctags(1)

map = create shortcut for command modemap = create shortcut for command mode

map! = create shortcut for insert modemap! = create shortcut for insert mode

r = read filer = read file

r! = read the output of execuabler! = read the output of execuable

sh = move to shellsh = move to shell

Interrupted system callInterrupted system call

Check chapter 10.5 in advanced Check chapter 10.5 in advanced programming in the unix environmentprogramming in the unix environment

Also do man select and check EINTRAlso do man select and check EINTR

Basicly if you get a signal such a SIGCHLD Basicly if you get a signal such a SIGCHLD select will fail. This is condition you have to select will fail. This is condition you have to check but you don’t have to die (actually you check but you don’t have to die (actually you should not die) should not die)

SyslogSyslog

In order for syslog to work you need to use In order for syslog to work you need to use LOG_LOCAL5 as facility (in openlog(3))LOG_LOCAL5 as facility (in openlog(3))

Because syslog didn’t work initially we Because syslog didn’t work initially we accepted file logging (but syslog is now accepted file logging (but syslog is now required for homework 2)required for homework 2)

The log file is at /var/log/messagesThe log file is at /var/log/messages