更改文件的属性

Question

我编写了一个改变文件属性的程序。我怎样才能提高程序的效率？请找出程序问题。我如何改进这个程序？

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/fs.h>

typedef enum {
    ActionNone_e,
    ADD_e, REMOVE_e, SET_e,
    ActionEnd_e,
} Action_e;

static void usage (const char *cmd_p);
static void process_mode (const char *modeStr_p, Action_e *actionRet_p, int *attrRet_p);

int
main (int argc, char *argv[])
{
    Action_e action;
    int attr, i, fd, ret, oldAttr;

    if (argc <= 2) {
        usage (argv[0]);
        return 1;
    }

    process_mode (argv[1], &action, &attr);
    if ((action <= ActionNone_e) || (action >= ActionEnd_e)) {
        printf ("mode must start with an action, which must be one of [-+=]\n");
        usage (argv[0]);
        return 1;
    }

    for (i=2; i<argc; ++i) {
        fd = open (argv[i], 0);
        if (fd == -1) {
            perror ("open()");
            return 1;
        }

        if ((action == ADD_e) || (action == REMOVE_e)) {
            ret = ioctl (fd, FS_IOC_GETFLAGS, &oldAttr);
            if (ret == -1) {
                perror ("ioctl(GET)");
                return 1;
            }
            if (action == ADD_e)
                attr |= oldAttr;
            if (action == REMOVE_e)
                attr = oldAttr & ~attr;
        }
        ret = ioctl (fd, FS_IOC_SETFLAGS, &attr);
        if (ret == -1)
            perror ("ioctl(SET)");
    }

    return 0;
}

static void
process_mode (const char *modeStr_p, Action_e *actionRet_p, int *attrRet_p)
{
    size_t len, i;
    Action_e action;
    int attr;

    if (modeStr_p == NULL)
        return;
    action = ActionNone_e;
    attr = 0;

    len = strlen (modeStr_p);
    if (len > 16)
        return;

    for (i=0; i<len; ++i) {
        switch (modeStr_p[i]) {
            case '+':
                action = ADD_e;
                break;

            case '-':
                action = REMOVE_e;
                break;

            case '=':
                action = SET_e;
                break;

            case 'a':
                attr |= FS_APPEND_FL;
                break;

            case 'c':
                attr |= FS_COMPR_FL;
                break;

            case 'D':
                attr |= FS_DIRSYNC_FL;
                break;

            case 'i':
                attr |= FS_IMMUTABLE_FL;
                break;

            case 'j':
                attr |= FS_JOURNAL_DATA_FL;
                break;

            case 'A':
                attr |= FS_NOATIME_FL;
                break;

            case 'd':
                attr |= FS_NODUMP_FL;
                break;

            case 't':
                attr |= FS_NOTAIL_FL;
                break;

            case 's':
                attr |= FS_SECRM_FL;
                break;

            case 'S':
                attr |= FS_SYNC_FL;
                break;

            case 'T':
                attr |= FS_TOPDIR_FL;
                break;

            case 'u':
                attr |= FS_UNRM_FL;
                break;

            case 'e':
                attr |= FS_EXTENT_FL;
                break;

            default:
                printf ("unknown flag: '%c' (0x%08x)\n", modeStr_p[i], modeStr_p[i]);
                break;
        }
    }

    if (actionRet_p != NULL)
        *actionRet_p = action;
    if (attrRet_p != NULL)
        *attrRet_p = attr;

}

static void
usage (const char *cmd_p)
{
    printf ("usage: %s <mode> <files...>\n", cmd_p);
    printf ("  change file attributes on a Linux file system\n");
    printf ("  <mode> -> +-=[acdeijstuADST]\n");
    printf ("    + -> adds mode\n");
    printf ("    - -> removes mode\n");
    printf ("    = -> sets mode\n");
    printf ("    a -> append only\n");
    printf ("    c -> compressed\n");
    printf ("    d -> no dump\n");
    printf ("    e -> extent format\n");
    printf ("    i -> immutable\n");
    printf ("    j -> data journalling\n");
    printf ("    s -> secure deletion\n");
    printf ("    t -> no tail-merging\n");
    printf ("    u -> undeletable\n");
    printf ("    A -> no atime updates\n");
    printf ("    D -> synchronous directory updates\n");
    printf ("    S -> synchronous updates\n");
    printf ("    T -> top of directory hierarchy\n");
} 

Answer 1

• 错误消息"mode must start with an action, which must be one of [-+=]\n"是误导性的。processMode愉快地在参数中的任何位置找到一个动作字符，而不一定是在开始时。我建议使用两个命令行参数，操作和模式，并独立处理它们。
• printfs在usage()中的一堆在代码大小和执行时间上都是次优的。一个对printf的调用就足够了: printf(“使用：%s \n”)“更改Linux文件系统上的文件属性\n”.)；编译器将将这些相邻字符串连接到一个单独的字符串中。
• 我不确定检查论点的长度是否正确。具体来说，我非常不喜欢神奇的数字16。如果您想要允许更多的标志(如当前缺少的FS_NOCOW_FL或FS_PROJINHERIT_FL )，则必须将16更改为其他标记。避免双重维修。