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File System Info C Functions

Declared in:  be/kernel/fs_info.h
Library: libroot.so
Summary:  more...


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


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


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:

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

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


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