1 /***************************************************************************
2 * Copyright (c) 2024 Microsoft Corporation
3 *
4 * This program and the accompanying materials are made available under the
5 * terms of the MIT License which is available at
6 * https://opensource.org/licenses/MIT.
7 *
8 * SPDX-License-Identifier: MIT
9 **************************************************************************/
10
11
12 /**************************************************************************/
13 /**************************************************************************/
14 /** */
15 /** FileX Component */
16 /** */
17 /** File */
18 /** */
19 /**************************************************************************/
20 /**************************************************************************/
21
22 #define FX_SOURCE_CODE
23
24
25 /* Include necessary system files. */
26
27 #include "fx_api.h"
28 #include "fx_system.h"
29 #include "fx_directory.h"
30 #include "fx_file.h"
31 #include "fx_utility.h"
32
33
34 /**************************************************************************/
35 /* */
36 /* FUNCTION RELEASE */
37 /* */
38 /* _fx_file_extended_relative_seek PORTABLE C */
39 /* 6.1 */
40 /* AUTHOR */
41 /* */
42 /* William E. Lamie, Microsoft Corporation */
43 /* */
44 /* DESCRIPTION */
45 /* */
46 /* This function positions the internal file pointers to the specified */
47 /* byte relative offset such that the next read or write operation is */
48 /* performed there. */
49 /* */
50 /* INPUT */
51 /* */
52 /* file_ptr File control block pointer */
53 /* byte_offset Byte offset of the seek */
54 /* seek_from Direction for relative seek, */
55 /* legal values are: */
56 /* */
57 /* FX_SEEK_BEGIN */
58 /* FX_SEEK_END */
59 /* FX_SEEK_FORWARD */
60 /* FX_SEEK_BACK */
61 /* */
62 /* OUTPUT */
63 /* */
64 /* return status */
65 /* */
66 /* CALLS */
67 /* */
68 /* _fx_file_extended_seek Seek to specified position */
69 /* */
70 /* CALLED BY */
71 /* */
72 /* Application Code */
73 /* */
74 /* RELEASE HISTORY */
75 /* */
76 /* DATE NAME DESCRIPTION */
77 /* */
78 /* 05-19-2020 William E. Lamie Initial Version 6.0 */
79 /* 09-30-2020 William E. Lamie Modified comment(s), */
80 /* resulting in version 6.1 */
81 /* */
82 /**************************************************************************/
_fx_file_extended_relative_seek(FX_FILE * file_ptr,ULONG64 byte_offset,UINT seek_from)83 UINT _fx_file_extended_relative_seek(FX_FILE *file_ptr, ULONG64 byte_offset, UINT seek_from)
84 {
85
86 #ifndef FX_MEDIA_STATISTICS_DISABLE
87 FX_MEDIA *media_ptr;
88
89 /* First, determine if the file is still open. */
90 if (file_ptr -> fx_file_id != FX_FILE_ID)
91 {
92
93 /* Return the file not open error status. */
94 return(FX_NOT_OPEN);
95 }
96
97 /* Setup pointer to media structure. */
98 media_ptr = file_ptr -> fx_file_media_ptr;
99
100 /* Increment the number of times this service has been called. */
101 media_ptr -> fx_media_file_relative_seeks++;
102 #endif
103
104 /* If trace is enabled, insert this event into the trace buffer. */
105 FX_TRACE_IN_LINE_INSERT(FX_TRACE_FILE_RELATIVE_SEEK, file_ptr, byte_offset, seek_from, file_ptr -> fx_file_current_file_offset, FX_TRACE_FILE_EVENTS, 0, 0)
106
107 /* Determine if seeking from the beginning is requested. */
108 if (seek_from == FX_SEEK_BEGIN)
109 {
110
111 /* Yes, use the base file seek routine to seek from the beginning of
112 the file. */
113 return(_fx_file_extended_seek(file_ptr, byte_offset));
114 }
115 /* Otherwise, determine if seeking from the end is requested. */
116 else if (seek_from == FX_SEEK_END)
117 {
118
119 /* Yes, seek from the end of the file. */
120
121 /* Determine if the requested seek offset is greater than
122 the file size. */
123 if (byte_offset >= file_ptr -> fx_file_current_file_size)
124 {
125
126 /* Yes, just seek to the beginning of the file. */
127 return(_fx_file_extended_seek(file_ptr, ((ULONG64) 0)));
128 }
129 else
130 {
131
132 /* Logically seek from the end of the file. */
133 return(_fx_file_extended_seek(file_ptr, file_ptr -> fx_file_current_file_size - byte_offset));
134 }
135 }
136 /* Otherwise, determine if seeking from the current position is requested. */
137 else if (seek_from == FX_SEEK_FORWARD)
138 {
139
140 /* Yes, just seek ahead from the current file position. */
141 return(_fx_file_extended_seek(file_ptr, file_ptr -> fx_file_current_file_offset + byte_offset));
142 }
143 /* Otherwise, seeking backward from the current position is assumed. */
144 else
145 {
146
147 /* Determine if the backward offset is greater than the current file offset. */
148 if (byte_offset >= file_ptr -> fx_file_current_file_offset)
149 {
150
151 /* Yes, just position the file to the beginning. */
152 return(_fx_file_extended_seek(file_ptr, ((ULONG64) 0)));
153 }
154 else
155 {
156
157 /* Seek backward relative to the current position. */
158 return(_fx_file_extended_seek(file_ptr, file_ptr -> fx_file_current_file_offset - byte_offset));
159 }
160 }
161 }
162
163
