struct dirent

[Emmanuel Blot]

Hi,

I have a quick question about the use of this structure.

It is defined as:

struct dirent {
ino_t d_fileno; /* file number of entry */
uint16_t d_reclen; /* length of this record */
uint16_t d_namlen; /* length of string in d_name */
uint8_t d_type; /* file type, see below */
#if defined(_NETBSD_SOURCE)
#define MAXNAMLEN 511 /* must be kept in sync with NAME_MAX */
char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */
#else
char d_name[511 + 1]; /* name must be no longer than this */
#endif
};

However, in servers/vfs/path.c get_name(), the temporary buffer to
receive the directory entries is allocated as follows:

#define DIR_ENTRIES 8
#define DIR_ENTRY_SIZE (sizeof(struct dirent) + NAME_MAX)
char buf[DIR_ENTRY_SIZE * DIR_ENTRIES];

and in fs/mfs/read.c getdents():

#define GETDENTS_BUFSIZE (sizeof(struct dirent) + MFS_NAME_MAX + 1)
#define GETDENTS_ENTRIES 8
static char getdents_buf[GETDENTS_BUFSIZE * GETDENTS_ENTRIES];

with:
#define NAME_MAX 511
#define MFS_DIRSIZ 60
#define MFS_NAME_MAX MFS_DIRSIZ

while lib/libfsdriver/dentry.c fsdriver_dentry_add() use d_dname to
store the directory entry name as expected, but limits its size to
MAXNAMLEN, and use d_reclen to increase the buffer pointer.

The question is: what are the extra bytes allocated in the temporary
buffer for (NAME_MAX && MFS_NAME_MAX)?

It would look like a leftover of another structure that would have
been defined as:

struct dirent {
ino_t d_fileno; /* file number of entry */
uint16_t d_reclen; /* length of this record */
uint16_t d_namlen; /* length of string in d_name */
uint8_t d_type; /* file type, see below */
char d_name[]; /* variable size */
};

- or am I missing something obvious?

Thanks,
Manu

[David van Moolenbroek]

Hey,

On Wednesday, February 25, 2015 at 6:20:55 PM UTC+1, Emmanuel Blot wrote:

It would look like a leftover of another structure that would have

been defined as: [..]

..and that is exactly what it is. :)

Regards,
David