在 fusexmp.c http://www.gtoal.com/fusestuff/fuse-2.7.0/example/fusexmp.c.html
有一行<<12
st.st_mode = de->d_type << 12;
请告诉我为什么左移 12 位
d_type 文件的类型,即:DT_UNKNOWN 我没有找到定义的位/usr/include/bits/dirent.h
谢谢
在 fusexmp.c http://www.gtoal.com/fusestuff/fuse-2.7.0/example/fusexmp.c.html
有一行<<12
st.st_mode = de->d_type << 12;
请告诉我为什么左移 12 位
d_type 文件的类型,即:DT_UNKNOWN 我没有找到定义的位/usr/include/bits/dirent.h
谢谢
位移从 dir-entryd_type
位域转换为使用的值 int struct stat.st_mode
:
# define IFTODT(mode) (((mode) & 0170000) >> 12)
# define DTTOIF(dirtype) ((dirtype) << 12)
文档可以简单地在 中找到man stat
,因为该值被分配给st_mode
结构stat
:
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
左移 12 位时的高位(对于信息,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