GETDIRENTRIESATTR(2)

NAME
getdirentriesattr - get file system attributes for multiple directory entries

SYNOPSIS
#include <sys/attr.h>
#include <unistd.h>
int
getdirentriesattr(int fd, struct attrlist * attrList, void * attrBuf, size_t attrBufSize, unsigned long * count, unsigned long * basep, unsigned long * newState, unsigned long options);

DESCRIPTION
The getdirentriesattr() function reads directory entries and returns their attributes (that is, metadata). You can think of it as a combination of getdirentries(2) and getattrlist(2). The function reads directory entries from the directory referenced by the file descriptor fd. Attributes of those directory entries are placed into the buffer specified by attrBuf and attrBufSize. The attrList parameter determines what attributes are returned for each entry. The count parameter contains the number of directory entries requested and returned. The basep parameter returns the directory offset in a manner similar to getdirentries(2). The newState parameter allows you to check whether the directory has been modified while you were reading it. The options parameter lets you control specific aspects of the function's behaviour.

The getdirentriesattr() function is only supported by certain volume format implementations. For maximum compatibility, client programs should use high-level APIs (such as the Carbon File Manager) to access file system attributes. These high-level APIs include logic to emulate file system attributes on volumes that don't support getdirentriesattr().

The fd parameter must be a file descriptor that references a directory that you have opened for reading.

The attrList parameter is a pointer to an attrlist structure. You are responsible for filling out all fields of this structure before calling the function. See the discussion of the getattrlist(2) function for a detailed description of this structure. To get an attribute you must set the corresponding bit in the appropriate attrgroup_t field of the attrlist structure. You must not request volume attributes.

The attrBuf and attrBufSize parameters specify a buffer into which the function places attribute values. The attributes for any given directory entry are grouped together and packed in exactly the same way as they are returned from getattrlist(2). These groups are then placed into the buffer, one after another. As each group starts with a leading unsigned long that contains the overall length of the group, you can step from one group to the next by simply adding this length to your pointer. The sample code (below) shows how to do this. The initial contents of this buffer are ignored.

The count parameter points to a unsigned long variable. You should initialise this variable to be the number of directory entries for which you wish to get attributes. On return, this variable contains the number of directory entries whose attributes have been placed into the attribute buffer. This may be smaller than the number that you requested.

The basep parameter returns the offset of the last directory entry read, in a manner identical to getdirentries(2). You can use this value to reset a directory iteration to a known position using lseek(2). The initial value of the variable is ignored.

The newState parameter returns a value that changes if the directory has been modified. If you're iterating through the directory by making repeated calls to getdirentriesattr(), you can compare subsequent values of newState to determine whether the directory has been modified (and thus restart your iteration at the beginning). The initial value of the variable is ignored.

The options parameter is a bit set that controls the behaviour of getdirentriesattr(). The following option bits are defined.

FSOPT_NOINMEMUPDATE
    This tells getdirentriesattr() to return the directory entries from disk rather than taking the extra step of looking at data structures in-memory which may contain changes that haven't been flushed to disk.

    This option allowed for specific performance optimizations for specific clients on older systems. We currently recommend that clients not set this option and that file system implementations ignore it.

It is typical to ask for a combination of common, file, and directory attributes and then use the value of the ATTR_CMN_OBJTYPE attribute to parse the resulting attribute buffer.

RETURN VALUES
Upon successful completion a value of 0 or 1 is returned. The value 0 indicates that the routine completed successfully. The value 1 indicates that the routine completed successfully and has returned the last entry in the directory. On error, a value of -1 is returned and errno is set to indicate the error.

COMPATIBILITY
Not all volumes support getdirentriesattr(). You can test whether a volume supports getdirentriesattr() by using getattrlist(2) to get the volume capabilities attribute ATTR_VOL_CAPABILITIES, and then testing the VOL_CAP_INT_READDIRATTR flag.

The getdirentriesattr() function has been undocumented for more than two years. In that time a number of volume format implementations have been created without a proper specification for the behaviour of this routine. You may encounter volume format implementations with slightly different behaviour than what is described here. Your program is expected to be tolerant of this variant behaviour.

If you're implementing a volume format that supports getdirentriesattr(), you should be careful to support the behaviour specified by this document.

ERRORS
getdirentriesattr() will fail if:

[ENOTSUP]
    The volume does not support getdirentriesattr().

[EBADF]
    fd is not a valid file descriptor for a directory open for reading.

[EFAULT]
    attrList or attrBuf points to an invalid address.

[EINVAL]
    The bitmapcount field of attrList is not ATTR_BIT_MAP_COUNT.

[EINVAL]
    You requested an invalid attribute.

[EINVAL]
    You requested volume attributes.

[EINVAL]
    The options parameter contains an invalid flag.

[EIO]
    An I/O error occurred while reading from or writing to the file system.

EXAMPLES
The following code lists the contents of a directory using getdirentriesattr(). The listing includes the file type and creator for files.

    #include <assert.h>
    #include <stdio.h>
    #include <stddef.h>
    #include <string.h>
    #include <sys/attr.h>
    #include <sys/errno.h>
    #include <unistd.h>
    #include <sys/vnode.h>
    #include <stdbool.h>
    #include <fcntl.h>

    typedef struct attrlist attrlist_t;

    struct FInfoAttrBuf {
        unsigned long   length;
        attrreference_t name;
        fsobj_type_t    objType;
        char            finderInfo[32];
    };
    typedef struct FInfoAttrBuf FInfoAttrBuf;

    enum {
        kEntriesPerCall = 10
    };

    static int FInfoDemo(const char *dirPath)
    {
        int             err;
        int             junk;
        int             dirFD;
        attrlist_t      attrList;
        unsigned long   index;
        unsigned long   count;
        unsigned long   junkBaseP;
        bool            oldStateValid;
        unsigned long   oldState;
        unsigned long   newState;
        bool            done;
        FInfoAttrBuf *  thisEntry;
        char            attrBuf[kEntriesPerCall * (sizeof(FInfoAttrBuf) + 64)];

        // attrBuf is big enough for kEntriesPerCall entries, assuming that
        // the average name length is less than 64.

        memset(&attrList, 0, sizeof(attrList));
        attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
        attrList.commonattr  =    ATTR_CMN_NAME
                                | ATTR_CMN_OBJTYPE
                                | ATTR_CMN_FNDRINFO;

        err = 0;
        dirFD = open(dirPath, O_RDONLY, 0);
        if (dirFD < 0) {
            err = errno;
        }
        if (err == 0) {
            oldStateValid = false;
            done = false;
            do {
                count = kEntriesPerCall;

                err = getdirentriesattr(
                    dirFD,
                    &attrList,
                    &attrBuf,
                    sizeof(attrBuf),
                    &count,
                    &junkBaseP,
                    &newState,
                    0
                );
                if (err < 0) {
                    err = errno;
                } else {
                    done = err;
                    err = 0;
                }

                if (err == 0) {
                    if (oldStateValid) {
                        if (newState != oldState) {
                            printf("*** Directory has changed\n");
                            oldState = newState;
                        }
                    } else {
                        oldState = newState;
                        oldStateValid = true;
                    }

                    thisEntry = (FInfoAttrBuf *) attrBuf;

                    for (index = 0; index < count; index++) {
                        switch (thisEntry->objType) {
                            case VREG:
                                printf(
                                    "'%4.4s' '%4.4s' ",
                                    &thisEntry->finderInfo[0],
                                    &thisEntry->finderInfo[4]
                                );
                                break;
                            case VDIR:
                                printf("directory     ");
                                break;
                            default:
                                printf(
                                    "objType = %-2d  ",
                                    thisEntry->objType
                                );
                                break;
                        }
                        printf(
                            "%s\n",
                            ((char *) &thisEntry->name)
                                + thisEntry->name.attr_dataoffset
                        );

                        // Advance to the next entry.

                        ((char *) thisEntry) += thisEntry->length;
                    }
                }
            } while ( err == 0 && ! done );
        }

        if (dirFD != -1) {
            junk = close(dirFD);
            assert(junk == 0);
        }

        return err;
    }

SEE ALSO
getattrlist(2), getdirentries(2), lseek(2)

HISTORY
A getdirentriesattr() function call appeared in Darwin 1.3.1 (Mac OS X version 10.0).