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fd-util: add new helper fd_reopen_conditional()

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This is a wrapper around fd_reopen() that will reopen an fd if the
F_GETFL flags indicate this is necessary, and otherwise not.

This is useful for various utility calls that shall be able to operate
on O_PATH and without it, and might need to convert between the two
depending on what's passed in.
This commit is contained in:
Lennart Poettering 2022-11-29 15:29:25 +01:00
parent 0461375326
commit 5f5865f0ad
3 changed files with 79 additions and 0 deletions
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31
src/basic/fd-util.c
View File

@ -780,6 +780,37 @@ int fd_reopen(int fd, int flags) {
return new_fd;
}
int fd_reopen_condition(
int fd,
int flags,
int mask,
int *ret_new_fd) {
int r, new_fd;
assert(fd >= 0);
/* Invokes fd_reopen(fd, flags), but only if the existing F_GETFL flags don't match the specified
* flags (masked by the specified mask). This is useful for converting O_PATH fds into real fds if
* needed, but only then. */
r = fcntl(fd, F_GETFL);
if (r < 0)
return -errno;
if ((r & mask) == (flags & mask)) {
*ret_new_fd = -1;
return fd;
}
new_fd = fd_reopen(fd, flags);
if (new_fd < 0)
return new_fd;
*ret_new_fd = new_fd;
return new_fd;
}
int read_nr_open(void) {
_cleanup_free_ char *nr_open = NULL;
int r;

1
src/basic/fd-util.h
View File

@ -108,6 +108,7 @@ static inline int make_null_stdio(void) {
})
int fd_reopen(int fd, int flags);
int fd_reopen_condition(int fd, int flags, int mask, int *ret_new_fd);
int read_nr_open(void);
int fd_get_diskseq(int fd, uint64_t *ret);

47
src/test/test-fd-util.c
View File

@ -483,6 +483,53 @@ TEST(fd_reopen) {
fd1 = -1;
}
TEST(fd_reopen_condition) {
_cleanup_close_ int fd1 = -1, fd3 = -1;
int fd2, fl;
/* Open without O_PATH */
fd1 = open("/usr/", O_RDONLY|O_DIRECTORY|O_CLOEXEC);
assert_se(fd1 >= 0);
fl = fcntl(fd1, F_GETFL);
assert_se(FLAGS_SET(fl, O_DIRECTORY));
assert_se(!FLAGS_SET(fl, O_PATH));
fd2 = fd_reopen_condition(fd1, O_DIRECTORY, O_DIRECTORY|O_PATH, &fd3);
assert_se(fd2 == fd1);
assert_se(fd3 < 0);
/* Switch on O_PATH */
fd2 = fd_reopen_condition(fd1, O_DIRECTORY|O_PATH, O_DIRECTORY|O_PATH, &fd3);
assert_se(fd2 != fd1);
assert_se(fd3 == fd2);
fl = fcntl(fd2, F_GETFL);
assert_se(FLAGS_SET(fl, O_DIRECTORY));
assert_se(FLAGS_SET(fl, O_PATH));
close_and_replace(fd1, fd3);
fd2 = fd_reopen_condition(fd1, O_DIRECTORY|O_PATH, O_DIRECTORY|O_PATH, &fd3);
assert_se(fd2 == fd1);
assert_se(fd3 < 0);
/* Switch off O_PATH again */
fd2 = fd_reopen_condition(fd1, O_DIRECTORY, O_DIRECTORY|O_PATH, &fd3);
assert_se(fd2 != fd1);
assert_se(fd3 == fd2);
fl = fcntl(fd2, F_GETFL);
assert_se(FLAGS_SET(fl, O_DIRECTORY));
assert_se(!FLAGS_SET(fl, O_PATH));
close_and_replace(fd1, fd3);
fd2 = fd_reopen_condition(fd1, O_DIRECTORY, O_DIRECTORY|O_PATH, &fd3);
assert_se(fd2 == fd1);
assert_se(fd3 < 0);
}
TEST(take_fd) {
_cleanup_close_ int fd1 = -1, fd2 = -1;
int array[2] = { -1, -1 }, i = 0;