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linux - 为什么在 fusexmp 中为 d_type 移动 12 位

转载 作者:太空狗 更新时间:2023-10-29 12:06:54 26 4
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在 fusexmp.c 中 http://www.gtoal.com/fusestuff/fuse-2.7.0/example/fusexmp.c.html

有一行<<12

st.st_mode = de->d_type << 12;

请指点一下为什么左移12位

d_type 文件的类型,即:DT_UNKNOWN我没有在 /usr/include/bits/dirent.h

中找到定义的位

谢谢

最佳答案

移位从目录条目d_type转换而来位域到使用的值 int struct stat.st_mode :

# define IFTODT(mode)   (((mode) & 0170000) >> 12)
# define DTTOIF(dirtype) ((dirtype) << 12)

文档可以简单地在 man stat 中找到,因为值被分配给 st_modestat结构:

The following flags are defined for the st_mode field:

S_IFMT 0170000 bit mask for the file type bit fields
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
S_ISUID 0004000 set UID bit
S_ISGID 0002000 set-group-ID bit (see below)
S_ISVTX 0001000 sticky bit (see below)
S_IRWXU 00700 mask for file owner permissions
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 mask for group permissions
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 mask for permissions for others (not in group)
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission

显然,de->d_type相当于st_mode的高位当左移 12 位时(信息,1<<12 == 0x1000)。 man readdir 救援:

现在完整的转换和位掩码在 sys/dirent.h 中:

/* File types for `d_type'.  */
enum
{
DT_UNKNOWN = 0, // The file type is unknown
DT_FIFO = 1, // This is a named pipe (FIFO).
DT_CHR = 2, // This is a character device.
DT_DIR = 4, // This is directory.
DT_BLK = 6, // This is a block device.
DT_REG = 8, // This is a regular file.
DT_LNK = 10, // This is a symbolic link.
DT_SOCK = 12, // This is a Unix domain socket.
DT_WHT = 14 // DT_CHR | DT_DIR | DT_REG
};

/* Convert between stat structure types and directory types. */
# define IFTODT(mode) (((mode) & 0170000) >> 12)
# define DTTOIF(dirtype) ((dirtype) << 12)
#endif

关于linux - 为什么在 fusexmp 中为 d_type 移动 12 位,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/8420234/

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