aboutsummaryrefslogtreecommitdiff
path: root/fmlock.c
blob: 45bb419768f02ec03c31f579769c5eecc32b356e (plain)
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
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/resource.h>
#include <stdio.h>
#include <unistd.h>
#include <stddef.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>

int heat_the_cache(int fd)
{
	char buf[1024];
	int rv;
	do {
	retry_read:
		rv = read(fd, buf, sizeof(buf));
		if( -1 == rv
		 && EINTR == errno ) {
			goto retry_read;
		}
	} while( 0 < rv );

	return rv != 0;
}

int main(int argc, char *argv[])
{
	unsigned long long locked_memory;
	int i, fd_null;
	fd_set phony_fdset;
	struct rlimit mlock_limit;

	if( 2 > argc ) {
		fprintf(stderr,
			"Usage:\n\n"
			"%s [filenames]\n\n"
			"Once its deed is done kill the process by sending a terminating signal.\n"
			"SIGINT (Ctrl+C) on the controlling terminal should do the trick.\n",
			argv[0] );
		return 1;
	}

	if( -1 == getrlimit(RLIMIT_MEMLOCK, &mlock_limit) ) {
		fprintf(stderr,
			"error getrlimit(RLIMIT_MEMLOCK): %s\n",
			strerror(errno) );
		return 1;
	}
	fprintf(stderr,
		"memlock rlimit: %llu\n",
		(unsigned long long)mlock_limit.rlim_cur );

	locked_memory = 0;
	for(i = 1; i < argc; ++i) {
		char const * const filename = argv[i];
		int fd;
		struct stat st;
		void *ptr;

		fprintf(stderr,
			"mlocking '%s'... ", filename);

	retry_open:
		fd = open(filename, O_RDONLY);
		if( -1 == fd ) {
			if( EINTR == errno ) {
				goto retry_open;
			} else
			{
				fprintf(stderr,
					"error open('%s'): %s\n",
					filename,
					strerror(errno) );
				continue;
			}
		}

		if( -1 == fstat(fd, &st) ) {
			fprintf(stderr,
				"error fstat(fd['%s']): %s\n",
				filename,
				strerror(errno) );
			goto finish_file;
		}

		if( locked_memory + st.st_size > mlock_limit.rlim_cur ) {
			fprintf(stderr,
				"error: exceeded the memlock resource limit for this process.\n"
				"Required limit to mlock '%s': %llu (counting already mlocked files)\n"
				"Locked memory resource limit set to: %llu\n"
				"Increase the locked memory resource limit and try again.\n",
				filename,
				(unsigned long long)locked_memory + st.st_size,
				(unsigned long long)mlock_limit.rlim_cur );
			close(fd);
			break;
		}

		ptr = mmap(
			NULL,
			st.st_size,
			PROT_READ,
			MAP_SHARED | MAP_LOCKED,
			fd,
			0 );
		if( MAP_FAILED == ptr ) {
			fprintf(stderr,
				"error mmap(fd['%s'], 0..%lld): %s\n",
				filename,
				(long long)st.st_size,
				strerror(errno) );
			goto finish_file;
		}

		if( -1 == mlock(ptr, st.st_size) ) {
			fprintf(stderr,
				"error mlock(ptr[fd['%s']]=%p): %s\n",
				filename,
				ptr,
				strerror(errno) );
			goto finish_file;
		}

		if( locked_memory + st.st_size < locked_memory ) {
			/* overflow */
			locked_memory = -1;
		} else
		{
			locked_memory += st.st_size;
		}

		heat_the_cache(fd);

	finish_file:
		close(fd);
		fputs("done\n", stderr);
	}

	if( !locked_memory ) {
		fprintf(stderr,
			"nothing locked, exiting.\n");
		return 1;
	}

	fprintf(stderr,
		"Files locked and cache heated up. pid=%lld. Going to sleep, .zZ...\n",
		(long long)getpid() );

	/* At this point the program shall sleep until a terminating
	 * signal arrives. To do so a nice side effect of the definition
	 * of /dev/null behavior is used: read on a /dev/null fd always
	 * return 0, which correspond to EOF which is a "no content
	 * available for read (yet)" situation for which select waits.
	 * So by selecting for a read a fd on /dev/null we can put the
	 * process to sleep. */
	fd_null = open("/dev/null", O_RDONLY);
	if( -1 == fd_null ) {
		fprintf(stderr,
			"error open('/dev/null'): %s\n",
			strerror(errno) );
		return 1;
	}
	FD_ZERO(&phony_fdset);
	FD_SET(fd_null, &phony_fdset);
	if( -1 == select(fd_null, &phony_fdset, NULL, NULL, NULL) ) {
		fprintf(stderr,
			"error select(...): %s\n",
			strerror(errno) );
		return 1;
	}

	return 0;
}