1 /* An interface to read and write that retries (if necessary) until complete.
2
3 Copyright (C) 1993-1994, 1997-2006, 2009-2021 Free Software Foundation, Inc.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 #include <config.h>
19
20 /* Specification. */
21 #ifdef FULL_READ
22 # include "full-read.h"
23 #else
24 # include "full-write.h"
25 #endif
26
27 #include <errno.h>
28
29 #ifdef FULL_READ
30 # include "safe-read.h"
31 # define safe_rw safe_read
32 # define full_rw full_read
33 # undef const
34 # define const /* empty */
35 #else
36 # include "safe-write.h"
37 # define safe_rw safe_write
38 # define full_rw full_write
39 #endif
40
41 #ifdef FULL_READ
42 /* Set errno to zero upon EOF. */
43 # define ZERO_BYTE_TRANSFER_ERRNO 0
44 #else
45 /* Some buggy drivers return 0 when one tries to write beyond
46 a device's end. (Example: Linux 1.2.13 on /dev/fd0.)
47 Set errno to ENOSPC so they get a sensible diagnostic. */
48 # define ZERO_BYTE_TRANSFER_ERRNO ENOSPC
49 #endif
50
51 /* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
52 interrupted or if a partial write(read) occurs. Return the number
53 of bytes transferred.
54 When writing, set errno if fewer than COUNT bytes are written.
55 When reading, if fewer than COUNT bytes are read, you must examine
56 errno to distinguish failure from EOF (errno == 0). */
57 size_t
full_rw(int fd,const void * buf,size_t count)58 full_rw (int fd, const void *buf, size_t count)
59 {
60 size_t total = 0;
61 const char *ptr = (const char *) buf;
62
63 while (count > 0)
64 {
65 size_t n_rw = safe_rw (fd, ptr, count);
66 if (n_rw == (size_t) -1)
67 break;
68 if (n_rw == 0)
69 {
70 errno = ZERO_BYTE_TRANSFER_ERRNO;
71 break;
72 }
73 total += n_rw;
74 ptr += n_rw;
75 count -= n_rw;
76 }
77
78 return total;
79 }
80