1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
|
/*-------------------------------------------------------------------------
*
* pg_iovec.h
* Header for vectored I/O functions, to use in place of <sys/uio.h>.
*
* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/port/pg_iovec.h
*
*-------------------------------------------------------------------------
*/
#ifndef PG_IOVEC_H
#define PG_IOVEC_H
#ifndef WIN32
#include <limits.h>
#include <sys/uio.h>
#include <unistd.h>
#else
/* POSIX requires at least 16 as a maximum iovcnt. */
#define IOV_MAX 16
/* Define our own POSIX-compatible iovec struct. */
struct iovec
{
void *iov_base;
size_t iov_len;
};
#endif
/* Define a reasonable maximum that is safe to use on the stack. */
#define PG_IOV_MAX Min(IOV_MAX, 32)
/*
* Like preadv(), but with a prefix to remind us of a side-effect: on Windows
* this changes the current file position.
*/
static inline ssize_t
pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#if HAVE_DECL_PREADV
/*
* Avoid a small amount of argument copying overhead in the kernel if
* there is only one iovec.
*/
if (iovcnt == 1)
return pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
else
return preadv(fd, iov, iovcnt, offset);
#else
ssize_t sum = 0;
ssize_t part;
for (int i = 0; i < iovcnt; ++i)
{
part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
if (part < 0)
{
if (i == 0)
return -1;
else
return sum;
}
sum += part;
offset += part;
if ((size_t) part < iov[i].iov_len)
return sum;
}
return sum;
#endif
}
/*
* Like pwritev(), but with a prefix to remind us of a side-effect: on Windows
* this changes the current file position.
*/
static inline ssize_t
pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#if HAVE_DECL_PWRITEV
/*
* Avoid a small amount of argument copying overhead in the kernel if
* there is only one iovec.
*/
if (iovcnt == 1)
return pwrite(fd, iov[0].iov_base, iov[0].iov_len, offset);
else
return pwritev(fd, iov, iovcnt, offset);
#else
ssize_t sum = 0;
ssize_t part;
for (int i = 0; i < iovcnt; ++i)
{
part = pg_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset);
if (part < 0)
{
if (i == 0)
return -1;
else
return sum;
}
sum += part;
offset += part;
if ((size_t) part < iov[i].iov_len)
return sum;
}
return sum;
#endif
}
#endif /* PG_IOVEC_H */
|
