summaryrefslogtreecommitdiff
path: root/internal/syscallcompat/emulate.go
blob: 35e17c655605ac4b48c45dfabb0e5e2c811ec314 (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
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
package syscallcompat

import (
	"os"
	"path/filepath"
	"sync"
	"syscall"

	"golang.org/x/sys/unix"
)

var chdirMutex sync.Mutex

// emulateRenameat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateRenameat(olddirfd int, oldpath string, newdirfd int, newpath string) error {
	chdirMutex.Lock()
	defer chdirMutex.Unlock()
	// Unless both paths are absolute we have to save the old working dir and
	// Chdir(oldWd) back to it in the end. If we error out before the first
	// chdir, Chdir(oldWd) is unneccassary but does no harm.
	if !filepath.IsAbs(oldpath) || !filepath.IsAbs(newpath) {
		oldWd, err := os.Getwd()
		if err != nil {
			return err
		}
		defer os.Chdir(oldWd)
	}
	// Make oldpath absolute
	oldpath, err := dirfdAbs(olddirfd, oldpath)
	if err != nil {
		return err
	}
	// Make newpath absolute
	newpath, err = dirfdAbs(newdirfd, newpath)
	if err != nil {
		return err
	}
	return syscall.Rename(oldpath, newpath)
}

// emulateUnlinkat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateUnlinkat(dirfd int, path string, flags int) (err error) {
	if !filepath.IsAbs(path) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(dirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	if (flags & unix.AT_REMOVEDIR) != 0 {
		return syscall.Rmdir(path)
	}
	return syscall.Unlink(path)
}

// emulateMknodat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateMknodat(dirfd int, path string, mode uint32, dev int) error {
	if !filepath.IsAbs(path) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(dirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	return syscall.Mknod(path, mode, dev)
}

// dirfdAbs transforms the dirfd-relative "path" to an absolute one. If the
// path is not already absolute, this function will change the working
// directory. The caller has to chdir back.
func dirfdAbs(dirfd int, path string) (string, error) {
	if filepath.IsAbs(path) {
		return path, nil
	}
	err := syscall.Fchdir(dirfd)
	if err != nil {
		return "", err
	}
	wd, err := os.Getwd()
	if err != nil {
		return "", err
	}
	return filepath.Join(wd, path), nil
}

// emulateFchmodat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateFchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
	if !filepath.IsAbs(path) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(dirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	// We also don't have Lchmod, so emulate it (poorly).
	if flags&unix.AT_SYMLINK_NOFOLLOW != 0 {
		fi, err := os.Lstat(path)
		if err != nil {
			return err
		}
		if fi.Mode()&os.ModeSymlink != 0 {
			return nil
		}
	}
	return syscall.Chmod(path, mode)
}

// emulateFchownat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateFchownat(dirfd int, path string, uid int, gid int, flags int) (err error) {
	if !filepath.IsAbs(path) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(dirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	return syscall.Lchown(path, uid, gid)
}

// emulateSymlinkat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateSymlinkat(oldpath string, newdirfd int, newpath string) (err error) {
	if !filepath.IsAbs(newpath) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(newdirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	return syscall.Symlink(oldpath, newpath)
}

// emulateMkdirat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateMkdirat(dirfd int, path string, mode uint32) (err error) {
	if !filepath.IsAbs(path) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(dirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	return syscall.Mkdir(path, mode)
}

// emulateFstatat emulates the syscall for platforms that don't have it
// in the kernel (darwin).
func emulateFstatat(dirfd int, path string, stat *unix.Stat_t, flags int) (err error) {
	if !filepath.IsAbs(path) {
		chdirMutex.Lock()
		defer chdirMutex.Unlock()
		cwd, err := syscall.Open(".", syscall.O_RDONLY, 0)
		if err != nil {
			return err
		}
		defer syscall.Close(cwd)
		err = syscall.Fchdir(dirfd)
		if err != nil {
			return err
		}
		defer syscall.Fchdir(cwd)
	}
	return unix.Lstat(path, stat)
}