File System Info C Functions

Declared in: be/kernel/fs_info.h

Library: libroot.so

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.