Low-level probing

Low-level probing — low-level prober initialization

Functions

Types and Values

typedef blkid_probe

Description

The low-level probing routines always and directly read information from the selected (see blkid_probe_set_device()) device.

The probing routines are grouped together into separate chains. Currently, the library provides superblocks, partitions and topology chains.

The probing routines is possible to filter (enable/disable) by type (e.g. fstype "vfat" or partype "gpt") or by usage flags (e.g. BLKID_USAGE_RAID). These filters are per-chain. Note that always when you touch the chain filter the current probing position is reset and probing starts from scratch. It means that the chain filter should not be modified during probing, for example in loop where you call blkid_do_probe().

For more details see the chain specific documentation.

The low-level API provides two ways how access to probing results.

  1. The NAME=value (tag) interface. This interface is older and returns all data as strings. This interface is generic for all chains.

  2. The binary interfaces. These interfaces return data in the native formats. The interface is always specific to the probing chain.

    Note that the previous probing result (binary or NAME=value) is always zeroized when a chain probing function is called. For example:

overwrites the previous probing result for the partitions chain, the superblocks result is not modified.

Functions

blkid_free_probe ()

void
blkid_free_probe (blkid_probe pr);

Deallocates the probe struct, buffers and all allocated data that are associated with this probing control struct.

Parameters

pr

probe

 

blkid_new_probe ()

blkid_probe
blkid_new_probe (void);

Returns

a pointer to the newly allocated probe struct or NULL in case of error.


blkid_new_probe_from_filename ()

blkid_probe
blkid_new_probe_from_filename (const char *filename);

This function is same as call open(filename), blkid_new_probe() and blkid_probe_set_device(pr, fd, 0, 0).

The filename is closed by blkid_free_probe() or by the blkid_probe_set_device() call.

Parameters

filename

device or regular file

 

Returns

a pointer to the newly allocated probe struct or NULL in case of error.


blkid_probe_get_devno ()

dev_t
blkid_probe_get_devno (blkid_probe pr);

Parameters

pr

probe

 

Returns

block device number, or 0 for regular files.


blkid_probe_get_fd ()

int
blkid_probe_get_fd (blkid_probe pr);

Parameters

pr

probe

 

Returns

file descriptor for assigned device/file or -1 in case of error.


blkid_probe_get_offset ()

blkid_loff_t
blkid_probe_get_offset (blkid_probe pr);

This function returns offset of probing area as defined by blkid_probe_set_device().

Parameters

pr

probe

 

Returns

offset in bytes or -1 in case of error.


blkid_probe_get_sectors ()

blkid_loff_t
blkid_probe_get_sectors (blkid_probe pr);

Parameters

pr

probe

 

Returns

512-byte sector count or -1 in case of error.


blkid_probe_get_sectorsize ()

unsigned int
blkid_probe_get_sectorsize (blkid_probe pr);

Parameters

pr

probe or NULL (for NULL returns 512)

 

Returns

block device logical sector size (BLKSSZGET ioctl, default 512).


blkid_probe_get_size ()

blkid_loff_t
blkid_probe_get_size (blkid_probe pr);

This function returns size of probing area as defined by blkid_probe_set_device(). If the size of the probing area is unrestricted then this function returns the real size of device. See also blkid_get_dev_size().

Parameters

pr

probe

 

Returns

size in bytes or -1 in case of error.


blkid_probe_get_wholedisk_devno ()

dev_t
blkid_probe_get_wholedisk_devno (blkid_probe pr);

Parameters

pr

probe

 

Returns

device number of the wholedisk, or 0 for regular files.


blkid_probe_is_wholedisk ()

int
blkid_probe_is_wholedisk (blkid_probe pr);

Parameters

pr

probe

 

Returns

1 if the device is whole-disk or 0.


blkid_probe_set_device ()

int
blkid_probe_set_device (blkid_probe pr,
                        int fd,
                        blkid_loff_t off,
                        blkid_loff_t size);

Assigns the device to probe control struct, resets internal buffers and resets the current probing.

Parameters

pr

probe

 

fd

device file descriptor

 

off

begin of probing area

 

size

size of probing area (zero means whole device/file)

 

Returns

-1 in case of failure, or 0 on success.


blkid_probe_step_back ()

int
blkid_probe_step_back (blkid_probe pr);

This function move pointer to the probing chain one step back -- it means that the previously used probing function will be called again in the next blkid_do_probe() call.

This is necessary for example if you erase or modify on-disk superblock according to the current libblkid probing result.

Example 1. wipe all superblock, but use libblkid only for probing

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pr = blkid_new_probe_from_filename(devname);

blkid_probe_enable_superblocks(pr, 1);
blkid_probe_set_superblocks_flags(pr, BLKID_SUBLKS_MAGIC);

blkid_probe_enable_partitions(pr, 1);
blkid_probe_set_partitions_flags(pr, BLKID_PARTS_MAGIC);

while (blkid_do_probe(pr) == 0) {
    const char *ostr = NULL;
    size_t len = 0;

    // superblocks
    if (blkid_probe_lookup_value(pr, "SBMAGIC_OFFSET", &ostr, NULL) == 0)
        blkid_probe_lookup_value(pr, "SBMAGIC", NULL, &len);

    // partition tables
    if (len == 0 && blkid_probe_lookup_value(pr, "PTMAGIC_OFFSET", &ostr, NULL) == 0)
        blkid_probe_lookup_value(pr, "PTMAGIC", NULL, &len);

    if (!len || !str)
        continue;

    // convert ostr to the real offset by off = strtoll(ostr, NULL, 10);
        // use your stuff to erase @len bytes at the @off
        ....

    // retry the last probing to check for backup superblocks ..etc.
        blkid_probe_step_back(pr);
}

Parameters

pr

prober

 

Returns

0 on success, and -1 in case of error.


blkid_reset_probe ()

void
blkid_reset_probe (blkid_probe pr);

Zeroize probing results and resets the current probing (this has impact to blkid_do_probe() only). This function does not touch probing filters and keeps assigned device.

Parameters

pr

probe

 

Types and Values

blkid_probe

typedef struct blkid_struct_probe *blkid_probe;

low-level probing setting