为什么在fusexmp中将12位换成d_type？

在fusexmp.c中http://www.gtoal.com/fusestuff/fuse-2.7.0/example/fusexmp.c.html

有一条线“12”

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

请指导我为什么左移12位

d_type文件的types，即：DT_UNKNowN我没有在/usr/include/bits/dirent.hfind定义的位

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谢谢

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位移由dir-entry d_type位字段转换为所使用的值int struct stat.st_mode ：

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

该文档只能在man stat找到，因为该值正在分配给stat结构体的st_mode ：

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，当左移12位时（对于info， 1<<12 == 0x1000 ）， de->d_type相当于de->d_type的高位。 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