Clarify the BIO_seek() mess and related issues.

Buffering BIO docs.

doc/crypto/BIO_ctrl.pod

@@ -47,8 +47,8 @@ BIO_reset() typically resets a BIO to some initial state, in the case
 of file related BIOs for example it rewinds the file pointer to the
 start of the file.
 
-BIO_seek() resets a file related BIO's file position pointer to B<ofs>
-bytes from start of file.
+BIO_seek() resets a file related BIO's (that is file descriptor and
+FILE BIOs) file position pointer to B<ofs> bytes from start of file.
 
 BIO_tell() returns the current file position of a file related BIO.
 
@@ -73,10 +73,12 @@ macros which call BIO_ctrl().
 
 =head1 RETURN VALUES
 
-BIO_reset() returns 1 for success and 0 for failure.
+BIO_reset() normally returns 1 for success and 0 or -1 for failure. File
+BIOs are an exception, they return 0 for success and -1 for failure.
 
 BIO_seek() and BIO_tell() both return the current file position on success
-and -1 for failure.
+and -1 for failure, except file BIOs which for BIO_seek() always return 0
+for success and -1 for failure.
 
 BIO_flush() returns 1 for success and 0 or -1 for failure.
 
@@ -102,14 +104,24 @@ case of a file BIO some data may be available in the FILE structures
 internal buffers but it is not possible to determine this in a
 portably way. For other types of BIO they may not be supported.
 
-Filter BIOs if the do not internally handle a particular BIO_ctrl()
+Filter BIOs if they do not internally handle a particular BIO_ctrl()
 operation usually pass the operation to the next BIO in the chain.
 This often means there is no need to locate the required BIO for
 a particular operation, it can be called on a chain and it will
-be automatically passed to the relevant BIO.
+be automatically passed to the relevant BIO. However this can cause
+unexpected results: for example no current filter BIOs implement
+BIO_seek(), but this may still succeed if the chain ends in a FILE
+or file descriptor BIO.
 
-Source/sink BIOs will return an error if the do not recognize the
-BIO_ctrl() operation.
+Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl()
+operation.
+
+=head1 BUGS
+
+Some of the return values are ambiguous and care should be taken. In
+particular a return value of 0 can be returned if an operation is not
+supported, if an error occurred, if EOF has not been reached and in
+the case of BIO_seek() on a file BIO for a successful operation. 
 
 =head1 SEE ALSO
 

doc/crypto/BIO_f_buffer.pod

@@ -0,0 +1,69 @@
+=pod
+
+=head1 NAME
+
+BIO_f_buffer - buffering BIO
+
+=head1 SYNOPSIS
+
+ #include <openssl/bio.h>
+
+ BIO_METHOD * BIO_f_buffer(void);
+
+ #define BIO_get_buffer_num_lines(b)	BIO_ctrl(b,BIO_C_GET_BUFF_NUM_LINES,0,NULL)
+ #define BIO_set_read_buffer_size(b,size) BIO_int_ctrl(b,BIO_C_SET_BUFF_SIZE,size,0)
+ #define BIO_set_write_buffer_size(b,size) BIO_int_ctrl(b,BIO_C_SET_BUFF_SIZE,size,1)
+ #define BIO_set_buffer_size(b,size)	BIO_ctrl(b,BIO_C_SET_BUFF_SIZE,size,NULL)
+ #define BIO_set_buffer_read_data(b,buf,num) BIO_ctrl(b,BIO_C_SET_BUFF_READ_DATA,num,buf)
+
+=head1 DESCRIPTION
+
+BIO_f_buffer() returns the buffering BIO method.
+
+Data written to a buffering BIO is buffered and periodically written
+to the next BIO in the chain. Data read from a buffering BIO comes from
+an internal buffer which is filled from the next BIO in the chain.
+Both BIO_gets() and BIO_puts() are supported.
+
+Calling BIO_reset() on a buffering BIO clears any buffered data.
+
+BIO_get_buffer_num_lines() returns the number of lines currently buffered.
+
+BIO_set_read_buffer_size(), BIO_set_write_buffer_size() and BIO_set_buffer_size()
+set the read, write or both read and write buffer sizes to B<size>. The initial
+buffer size is DEFAULT_BUFFER_SIZE, currently 1024. Any attempt to reduce the
+buffer size below DEFAULT_BUFFER_SIZE is ignored. Any buffered data is cleared
+when the buffer is resized.
+
+BIO_set_buffer_read_data() clears the read buffer and fills it with B<num>
+bytes of B<buf>. If B<num> is larger than the current buffer size the buffer
+is expanded.
+
+=head1 NOTES
+
+Buffering BIOs implement BIO_gets() by using BIO_read() operations on the
+next BIO in the chain. By prepending a buffering BIO to a chain it is therefore
+possible to provide BIO_gets() functionality if the following BIOs do not
+support it (for example SSL BIOs).
+
+Data is only written to the next BIO in the chain when the write buffer fills
+or when BIO_flush() is called. It is therefore important to call BIO_flush()
+whenever any pending data should be written such as when removing a buffering
+BIO using BIO_pop(). BIO_flush() may need to be retried if the ultimate
+source/sink BIO is non blocking.
+
+=head1 RETURN VALUES
+
+BIO_f_buffer() returns the buffering BIO method.
+
+BIO_get_buffer_num_lines() returns the number of lines buffered (may be 0).
+
+BIO_set_read_buffer_size(), BIO_set_write_buffer_size() and BIO_set_buffer_size()
+return 1 if the buffer was successfully resized or 0 for failure.
+
+BIO_set_buffer_read_data() returns 1 if the data was set correctly or 0 if
+there was an error.
+
+=head1 SEE ALSO
+
+TBA

doc/crypto/BIO_s_file.pod

@@ -38,7 +38,7 @@ BIO_reset() attempts to change the file pointer to the start of file
 using fseek(stream, 0, 0).
 
 BIO_seek() sets the file pointer to position B<ofs> from start of file
-using lseek(stream, ofs, 0).
+using fseek(stream, ofs, 0).
 
 BIO_eof() calls feof().
 
@@ -105,7 +105,7 @@ Alternative technique:
  BIO *out;
  out = BIO_new(BIO_s_file());
  if(out == NULL) /* Error ... */
- if(!BIO_read_filename(out, "filename.txt")) /* Error ... */
+ if(!BIO_write_filename(out, "filename.txt")) /* Error ... */
  BIO_printf(out, "Hello World\n");
  BIO_free(out);
 
@@ -127,6 +127,13 @@ BIO_tell() returns the current file position.
 BIO_read_filename(), BIO_write_filename(),  BIO_append_filename() and
 BIO_rw_filename() return 1 for success or 0 for failure.
 
+=head1 BUGS
+
+BIO_reset() and BIO_seek() are implemented using fseek() on the underlying
+stream. The return value for fseek() is 0 for success or -1 if an error
+occurred this differs from other types of BIO which will typically return
+1 for success and a non positive value if an error occurred.
+
 =head1 SEE ALSO
 
 L<BIO_seek(3)|BIO_seek(3)>, L<BIO_tell(3)|BIO_tell(3)>,