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

谢谢

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