File System Info C Functions

From time to time, it can be useful to know certain information about the capabilities of the file system on a device. While the BVolume class provides you easy access to this information, it can occasionally be helpful to have more direct access to this information.

This section describes three C functions which can be used to obtain information about the file system on a device. One of these functions, fs_stat_dev(), returns this information given a device number. The other two functions, dev_for_path() and next_dev(), provide two ways to obtain a device number for use with fs_stat_dev().

: Note that these functions don't set errno.

C Functions

dev_for_path()

 dev_t dev_for_path(const char *path)

: Given a pathname, returns the device number of the device on which the path is located. If the result is negative, it is a return code specifying an error.

: RETURN CODES

B_ENTRY_NOT_FOUND.,path does not exist, or is NULL or an empty string.
B_BAD_VALUE. path is null or an empty string.
B_NAME_TOO_LONG. path is too long.
B_NO_MEMORY. Insufficient memory to complete the operation.
B_FILE_ERROR. A file system error prevented the operation from succeeding.

next_dev()

 dev_t next_dev(int32 *pos)

: The next_dev() function allows you to iterate through all devices, receiving their device numbers as a result each time. If the result is negative, it is an error code. When the end of the device list is reached, the return value B_BAD_VALUE is returned.

: You should initially set pos to 0, then call next_dev() in a loop to obtain each device number until an error occurs. For example:

 void ScanDevices(void)
 { 
    int pos; 
    pos = 0; 

    while(next_dev(&pos) >=0)
    { 
        do_something(pos); 
    } 
 }

: RETURN CODES

B_BAD_VALUE. No matching device found.

fs_stat_dev()

 int fs_stat_dev(dev_t dev, fs_info *info)

 struct {} fs_info

: fs_stat_dev() returns information about the specified device. This can be used in conjunction with next_dev() to scan all devices and record information your application requires.

: This function returns 0 if the request was successful or -1 if an error occurred. Use the errno() function to determine what error in particular occurred.

: The fs_info structure is defined as:

 typedef struct fs_info
 { 
    dev_t       dev; 
    ino_t       root; 
    uint32      flags; 
    off_t       block_size; 
    off_t       io_size; 
    off_t       total_blocks; 
    off_t       free_blocks; 
    off_t       total_nodes; 
    off_t       free_nodes; 
    char        device_name[128]; 
    char        volume_name[B_FILE_NAME_LENGTH]; 
    char        fsh_name[B_OS_NAME_LENGTH]; 
 };

: The structure's fields are:

dev. The device number of the device.
root. The inode of the root of the device.
flags. Flags describing the device's capabilities.
block_size. The fundamental block size of the device.
io_size. Optimal I/O size of the device.
total_blocks. The total number of blocks on the device.
free_blocks. The number of free (unused) blocks on the device.
total_nodes. The total number of nodes on the device.
free_nodes. The number of free (unused) nodes on the device.
device_name. Name of the device holding the file system.
volume_name. Name of the volume contained by the device.
fsh_name. Name of the file system handler for the device.

: The flags can be any combination of the following values, which specify the attributes of the file system on the device:

B_FS_IS_READONLY. The file system on the device is read-only.
B_FS_IS_REMOVABLE. The device contains removable media.
B_FS_IS_PERSISTENT. Data written to the device remains even while the device is off.
B_FS_IS_SHARED. The file system is being shared on a network.
B_FS_HAS_MIME. The file system supports the MIME typing system used by the BeOS.
B_FS_HAS_ATTR. The file system supports node attributes.
B_FS_HAS_QUERY. THe file system supports the BeOS query mechanism.

: The information in the fs_info structure is guaranteed to be internally consistent, but the structure as a whole should be considered to be out-of-date as soon as you receive it. It provides a picture of a device as it exists just before the info-retrieving function returns. In particular, the number of free blocks and of free nodes can easily change immediately after you receive this information.

: RETURN CODES

B_OK. The device was found; info contains valid information.
B_BAD_VALUE. dev doesn't identify an existing device.