GETATTRLISTBULK(2) System Calls Manual GETATTRLISTBULK(2)

getattrlistbulk — get file system attributes for multiple directory entries

#include <sys/attr.h>
#include <unistd.h>


int
getattrlistbulk(int dirfd, struct attrlist * attrList, void * attrBuf, size_t attrBufSize, uint64_t options);

The () function iterates over the items in a directory and returns information about each directory entry like getattrlist(2). Note: when getattrlistbulk() returns information about a symbolic link, the information returned is about the link itself, not the target of the link. The order of the directory entries (and their associated metadata) vended by getattrlistbulk() is not specified. Some file systems may return entries in lexicographic sort order and others may not.

The function reads directory entries from the directory referenced by the file descriptor dirfd. The attrList parameter determines what attributes are returned for each entry. Attributes of those directory entries are placed into the buffer specified by attrBuf and attrBufSize. The options parameter allows you to modify the behaviour of the call.

The dirfd 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. All fields of this structure must be filled before calling the function. See the discussion of the getattrlist(2) function for a detailed description of this structure. To get an attribute, the corresponding bit in the appropriate attrgroup_t field of the attrlist structure must be set. Volume attributes cannot be requested but all other supported getattrlist attributes can be used. For this function, ATTR_CMN_NAME and ATTR_CMN_RETURNED_ATTRS are required and the absence of these attributes in the attrList parameter results in an error. Note that not all attributes supported by () may be vended back by this call, which is why the aforementioned flag must be supplied. In particular ATTR_CMN_FULLPATH may not be valid on all directory entries whose information is requested by this call.

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) and are subject to exactly the same alignment specifications and restrictions. These groups are then placed into the buffer, one after another. getattrlist(2) should be consulted on details of the attributes that can be requested for and returned. The name of the entry itself is provided by the ATTR_CMN_NAME attribute. Each group starts with a leading uint32_t , which will always be 8-byte aligned 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 options parameter is a bit set that controls the behaviour of (). The following option bits are defined.

FSOPT_PACK_INVAL_ATTRS
If this is bit is set, then all requested attributes, even ones that are not supported by the object or file file system, will be returned the attrBuf. The attributes actually returned can be determined by looking at the attribute_set_t structure returned for the ATTR_CMN_RETURNED_ATTRS attribute. Default values will be returned for invalid attributes and should be ignored.

Please see the discussion of this flag in getattrlist(2)

If ATTR_CMN_ERROR has been requested and an error specific to a directory entry occurs, an error will be reported. The ATTR_CMN_ERROR attribute is a uint32_t which, if non-zero, specifies the error code that was encountered during the processing of that directory entry. The ATTR_CMN_ERROR attribute will be after ATTR_CMN_RETURNED_ATTRS attribute in the returned buffer.

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.

A directory which is a mount point for a file system, will have a value of “DIR_MNTSTATUS_MNTPOINT” set for its ATTR_DIR_MOUNTSTATUS attribute entry. However the attributes for the mount point will be those from the (underlying) file system. To get the attributes of the mounted root directory, call getattrlist(2) on the mount point.

A directory which is a firmlink will have the “SF_FIRMLINK” flag set in its ATTR_CMN_FLAGS attribute entry. However, the attributes returned by () will be those from the firmlink, not the firmlink's target. To get the attribute of the firmlink's target, call getattrlist(2) on the firmlink.

Upon successful completion the numbers of entries successfully read is returned. A value of 0 indicates there are no more entries. Once 0 is returned, no further entries are returned even if new entries are added to the directory. Directory iteration should be restarted either by repostioning the offset to 0 by lseek() or by closing the file descriptor and opening the directory again. On error, a value of -1 is returned and errno is set to indicate the error.

When iterating all entries in a directory, getattrlistbulk() is called repeatedly until a 0 is returned. In such a case if readdir() and getattrlistbulk() calls on the same fd are mixed, the behavior is undefined.

getattrlistbulk() will fail if:

[]
dirfd is not a valid file descriptor for a directory open for reading.
[]
The File descriptor dirfd is not a directory.
[]
Search permission is denied on the directory whose descriptor is given as input.
[]
attrList or points to an invalid address.
[]
The buffer was too small.
[]
The bitmapcount field of attrList is not ATTR_BIT_MAP_COUNT.
[]
An invalid attribute was requested.
[]
Volume attributes were requested.
[]
or ATTR_CMN_RETURNED_ATTRS was not requested in the attrList parameter.
[]
An I/O error occurred while reading from or writing to the file system.

The following code lists the contents of a directory using getattrlistbulk(). The listing includes the file type.

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

typedef struct val_attrs {
    uint32_t          length;
    attribute_set_t   returned;
    uint32_t          error;
    attrreference_t   name_info;
    char              *name;
    fsobj_type_t      obj_type;
} val_attrs_t;


void demo(const char *dirpath)
{
    int error;
    int dirfd;
    struct attrlist attrList;
    char *entry_start;
    char attrBuf[256];

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

    error = 0;
    dirfd = open(dirpath, O_RDONLY, 0);
    if (dirfd < 0) {
        error = errno;
        printf("Could not open directory %s", dirpath);
        perror("Error was ");
    } else {
        for (;;) {
            int retcount;

            retcount = getattrlistbulk(dirfd, &attrList, &attrBuf[0],
                               sizeof(attrBuf), 0);
            printf("\ngetattrlistbulk returned %d", retcount);
            if (retcount == -1) {
                error = errno;
                perror("Error returned : ");
                printf("\n");
                break;
            } else if (retcount == 0) {
                /* No more entries in directory */
                error = 0;
                break;
            } else {
                int    index;
                uint32_t total_length;
                char   *field;

                entry_start = &attrBuf[0];
                total_length = 0;
                printf(" -> entries returned");
                for (index = 0; index < retcount; index++) {
                    val_attrs_t    attrs = {0};

                    printf("\n Entry %d", index);
                    printf("  --  ");
                    field = entry_start;
                    attrs.length = *(uint32_t *)field;
                    printf(" Length %d ", attrs.length);
                    total_length += attrs.length;
                    printf(" Total Length %d ", total_length);
                    field += sizeof(uint32_t);
                    printf("  --  ");

                    /* set starting point for next entry */
                    entry_start += attrs.length;

                    attrs.returned = *(attribute_set_t *)field;
                    field += sizeof(attribute_set_t);

                    if (attrs.returned.commonattr & ATTR_CMN_ERROR) {
                        attrs.error = *(uint32_t *)field;
                        field += sizeof(uint32_t);
                    }

                    if (attrs.returned.commonattr & ATTR_CMN_NAME) {
                        attrs.name =  field;
                        attrs.name_info = *(attrreference_t *)field;
                        field += sizeof(attrreference_t);
                        printf("  %s ", (attrs.name +
                            attrs.name_info.attr_dataoffset));
                    }

                    /* Check for error for this entry */
                    if (attrs.error) {
                        /*
                         * Print error and move on to next
                         * entry
                         */
                        printf("Error in reading attributes for directory                                entry %d", attrs.error);
                        continue;
                    }

                    printf("  --  ");
                    if (attrs.returned.commonattr & ATTR_CMN_OBJTYPE) {
                        attrs.obj_type = *(fsobj_type_t *)field;
                        field += sizeof(fsobj_type_t);

                        switch (attrs.obj_type) {
                            case VREG:
                                printf("file  ");
                                break;
                            case VDIR:
                                printf("directory    ");
                                break;
                            default:
                                printf("obj_type = %-2d  ", attrs.obj_type);
                                break;
                        }
                    }
                    printf("  --  ");
                }
            }
        }
        (void)close(dirfd);
    }
}

getattrlist(2), lseek(2)

A getattrlistbulk() function call appeared in OS X version 10.10

November 15, 2013 Darwin