disk.cpp

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#include "sfs/disk.h"
 
#include <stdexcept>
 
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
 
void Disk::open(const char *path, size_t nblocks) {
    FileDescriptor = ::open(path, O_RDWR|O_CREAT, 0600); 
    
    if (FileDescriptor < 0) {
        char what[BUFSIZ];
        snprintf(what, BUFSIZ, "Unable to open %s: %s", path, strerror(errno));
        throw std::runtime_error(what);
    }
 
    if (ftruncate(FileDescriptor, nblocks*BLOCK_SIZE) < 0) {
        char what[BUFSIZ];
        snprintf(what, BUFSIZ, "Unable to open %s: %s", path, strerror(errno));
        throw std::runtime_error(what);
    }
 
    Blocks = nblocks;
    Reads  = 0;
    Writes = 0;
}
 
Disk::~Disk() {
    if (FileDescriptor > 0) {
        printf("%lu disk block reads\n", Reads);
        printf("%lu disk block writes\n", Writes);
        close(FileDescriptor);
        FileDescriptor = 0;
    }
}
 
void Disk::sanity_check(int blocknum, char *data) {
    char what[BUFSIZ]; 
    if (blocknum < 0) {
        snprintf(what, BUFSIZ, "blocknum (%d) is negative!", blocknum);
        throw std::invalid_argument(what);
    }
 
    if (blocknum >= (int)Blocks) {
        snprintf(what, BUFSIZ, "blocknum (%d) is too big!", blocknum);
        throw std::invalid_argument(what);
    }
 
    if (data == NULL) {
        snprintf(what, BUFSIZ, "null data pointer!");
        throw std::invalid_argument(what);
    }
}
 
void Disk::read(int blocknum, char *data) {
    sanity_check(blocknum, data);
 
    if (lseek(FileDescriptor, blocknum*BLOCK_SIZE, SEEK_SET) < 0) {
        char what[BUFSIZ];
        snprintf(what, BUFSIZ, "Unable to lseek %d: %s", blocknum, strerror(errno));
        throw std::runtime_error(what);
    }
 
    if (::read(FileDescriptor, data, BLOCK_SIZE) != BLOCK_SIZE) {
        char what[BUFSIZ];
        snprintf(what, BUFSIZ, "Unable to read %d: %s", blocknum, strerror(errno));
        throw std::runtime_error(what);
    }
 
    Reads++;
}
 
void Disk::write(int blocknum, char *data) {
    sanity_check(blocknum, data);
 
    if (lseek(FileDescriptor, blocknum*BLOCK_SIZE, SEEK_SET) < 0) {
        char what[BUFSIZ];
        snprintf(what, BUFSIZ, "Unable to lseek %d: %s", blocknum, strerror(errno));
        throw std::runtime_error(what);
    }
 
    if (::write(FileDescriptor, data, BLOCK_SIZE) != BLOCK_SIZE) {
        char what[BUFSIZ];
        snprintf(what, BUFSIZ, "Unable to write %d: %s", blocknum, strerror(errno));
        throw std::runtime_error(what);
    }
 
    Writes++;
}