MESSAGE
| DATE | 2015-03-08 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [LIU Comp Sci] Re: Operating systems HW
|
From owner-learn-outgoing-at-mrbrklyn.com Sun Mar 8 20:24:50 2015
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Date: Sun, 08 Mar 2015 20:24:49 -0400
From: Ruben Safir
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To: mohammed Ghriga
Subject: [LIU Comp Sci] Re: Operating systems HW
References: <54FCE7DB.3000700-at-panix.com>
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BTW this was the question:
Programming Problems
2.26
In Section 2.3, we described a program that copies the contents of one file
to a destination file. This program works by first prompting the user for
the name of the source and destination files. Write this program using
either the Windows or POSIX API . Be sure to include all necessary error
checking, including ensuring that the source file exists.
Once you have correctly designed and tested the program, if you
used a system that supports it, run the program using a utility that traces
system calls. Linux systems provide the strace utility, and Solaris and
Mac OS X systems use the dtrace command. As Windows systems do
not provide such features, you will have to trace through the Windows
version of this program using a debugger.
One thing you notice is that the GNU optimizer is SMARTER than the C
strings library.
On 03/08/2015 08:22 PM, Ruben Safir wrote:
> I lost track of what the home work was, but before I moved forward
> answering quiz questions, I wanted to tackle some of the coding
> assignments in Chapter 2, because I thought I could learn a lot more
> from them. So I did read Cpt 2 and 3, but I wanted to finish this which
> was good because I completely forgot a number of things about fstat,
> fopen and the use of strace, I had never done that before actually
> although I am familiar and used extensively nm. I made a lot of
> blunders on the way to finishing this, but others might benefit from
> this as well. I'm going on to doing the kernel programming tonight, I
> hope and tackle chapter 3 'quiz' questions at school in the AM before class.
>
> Ruben
>
> #include
> #include
> #include
> #include
> #include
>
> char buf[500] = {0};
> char buf2[500] = {0};
> char * buf3;
> int fd, ret;
> size_t len;
> const char * PASSWD = "/etc/passwd";
> off_t tmpsize;
>
> struct stat filetmp;
>
> FILE * INPUT;
> FILE * OUTPUT;
> int main( int argc, char * argv[])
> {
> puts ("Enter a file to copy\n");
> if ( ! fgets( buf, 500, stdin) )
> return EXIT_FAILURE;
> len = strlen(buf);
> buf[len-1] = 0;
>
>
> puts ("Enter the file to copy to\n");
> if ( ! fgets( buf2, 500, stdin) )
> return EXIT_FAILURE;
> len = strlen(buf2);
> buf2[len-1] = 0;
>
> if( access( buf, F_OK|R_OK ) == 0 ) {
> INPUT = fopen( buf, "r");
> if (INPUT == NULL){
> printf("Can't Open %s\n", buf);
> exit(EXIT_FAILURE);
> }
> }else{
> perror("access INPUT file stat");
> exit (EXIT_FAILURE);
> }
> //File Opened for reading
> fd = fileno(INPUT);
> if (fstat(fd, &filetmp ) == -1){
> perror("stat on reading file:");
> exit(EXIT_FAILURE);
> }
> //FILE IS STATTED
> tmpsize = filetmp.st_size;
> if( (buf3 = (char *) malloc( sizeof(int) * tmpsize)) == NULL)
> exit (EXIT_FAILURE);
> ret = fread(buf3, tmpsize, 1, INPUT);
> if( ret != 1){
> fprintf(stderr, "Read not complete: Req ==> %d Rec ==> %zu \n",
> ret, tmpsize);
> exit(EXIT_FAILURE);
> }
>
> OUTPUT = fopen(buf2, "w");
> if(OUTPUT == NULL){
> printf("Can't Open %s\n ", buf2);
> exit(EXIT_FAILURE);
> }
> //File Open for Writing
> ret = fwrite(buf3, tmpsize, 1, OUTPUT);
> if(ret != 1){
> perror("WRITE");
> fprintf(stderr, "WRITE not complete: Req ==> %d Rec ==> %zu\n",
> ret, tmpsize);
> exit(EXIT_FAILURE);
> }
> free(buf3);
> fclose(INPUT);
> fclose(OUTPUT);
> return 1;
> }
>
> execve("./a.out", ["./a.out"], [/* 55 vars */]) = 0
> brk(0) = 0x68b000
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fdb000
> access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or
> directory)
> open("/home/ruben/GNUstep/Library/Libraries/tls/x86_64/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/home/ruben/GNUstep/Library/Libraries/tls/x86_64", 0x7fffd1634d10)
> = -1 ENOENT (No such file or directory)
> open("/home/ruben/GNUstep/Library/Libraries/tls/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/home/ruben/GNUstep/Library/Libraries/tls", 0x7fffd1634d10) = -1
> ENOENT (No such file or directory)
> open("/home/ruben/GNUstep/Library/Libraries/x86_64/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/home/ruben/GNUstep/Library/Libraries/x86_64", 0x7fffd1634d10) =
> -1 ENOENT (No such file or directory)
> open("/home/ruben/GNUstep/Library/Libraries/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/home/ruben/GNUstep/Library/Libraries", 0x7fffd1634d10) = -1
> ENOENT (No such file or directory)
> open("/root/GNUstep/Library/Libraries/tls/x86_64/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/root/GNUstep/Library/Libraries/tls/x86_64", 0x7fffd1634d10) = -1
> ENOENT (No such file or directory)
> open("/root/GNUstep/Library/Libraries/tls/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/root/GNUstep/Library/Libraries/tls", 0x7fffd1634d10) = -1 ENOENT
> (No such file or directory)
> open("/root/GNUstep/Library/Libraries/x86_64/libc.so.6",
> O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> stat("/root/GNUstep/Library/Libraries/x86_64", 0x7fffd1634d10) = -1
> ENOENT (No such file or directory)
> open("/root/GNUstep/Library/Libraries/libc.so.6", O_RDONLY|O_CLOEXEC) =
> -1 ENOENT (No such file or directory)
> stat("/root/GNUstep/Library/Libraries", 0x7fffd1634d10) = -1 ENOENT (No
> such file or directory)
> open("/usr/lib/tls/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT
> (No such file or directory)
> stat("/usr/lib/tls/x86_64", 0x7fffd1634d10) = -1 ENOENT (No such file or
> directory)
> open("/usr/lib/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such
> file or directory)
> stat("/usr/lib/tls", 0x7fffd1634d10) = -1 ENOENT (No such file or
> directory)
> open("/usr/lib/x86_64/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No
> such file or directory)
> stat("/usr/lib/x86_64", 0x7fffd1634d10) = -1 ENOENT (No such file or
> directory)
> open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
> read(3,
> "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`\1\2\0\0\0\0\0"..., 832)
> = 832
> fstat(3, {st_mode=S_IFREG|0755, st_size=1984416, ...}) = 0
> mmap(NULL, 3813200, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3,
> 0) = 0x7f71c0a18000
> mprotect(0x7f71c0bb1000, 2097152, PROT_NONE) = 0
> mmap(0x7f71c0db1000, 24576, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x199000) = 0x7f71c0db1000
> mmap(0x7f71c0db7000, 16208, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f71c0db7000
> close(3) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fda000
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fd9000
> arch_prctl(ARCH_SET_FS, 0x7f71c0fda700) = 0
> mprotect(0x7f71c0db1000, 16384, PROT_READ) = 0
> mprotect(0x7f71c0fdc000, 4096, PROT_READ) = 0
> fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fd8000
> write(1, "Enter a file to copy\n", 21) = 21
> write(1, "\n", 1) = 1
> fstat(0, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fd7000
> read(0, "/etc/passwd\n", 1024) = 12
> write(1, "Enter the file to copy to\n", 26) = 26
> write(1, "\n", 1) = 1
> read(0, "/home/ruben/ssadsa.tmp\n", 1024) = 23
> access("/etc/passwd", R_OK) = 0
> brk(0) = 0x68b000
> brk(0x6ac000) = 0x6ac000
> open("/etc/passwd", O_RDONLY) = 3
> fstat(3, {st_mode=S_IFREG|0644, st_size=1637, ...}) = 0
> fstat(3, {st_mode=S_IFREG|0644, st_size=1637, ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fd6000
> read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1637
> open("/home/ruben/ssadsa.tmp", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 5
> fstat(5, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> = 0x7f71c0fd5000
> close(3) = 0
> munmap(0x7f71c0fd6000, 4096) = 0
> write(5, "root:x:0:0:root:/root:/bin/bash\n"..., 1637) = 1637
> close(5) = 0
> munmap(0x7f71c0fd5000, 4096) = 0
> exit_group(1) = ?
> +++ exited with 1 +++
>
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