From 67387626884afec7dbb64cb78a39a3676b7ff663 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Fri, 27 Feb 2026 10:05:16 +0100 Subject: [PATCH] fileio: introduce write_data_file_atomic_at() helper This is very similar to write_string_file_atomic(), but is intentionally kept separate (after long consideration). It focusses on arbitrary struct iovec data, not just strings, and hence also doesn't do stdio at all. It's hence a lot more low-level. We might want to consider moving write_string_file*() on top of write_data_file_atomic_at(), but for now don't. --- src/basic/fileio.c | 62 ++++++++++++++++++++++++++++++++++++++++++ src/basic/fileio.h | 6 ++++ src/test/test-fileio.c | 52 +++++++++++++++++++++++++++++++++++ 3 files changed, 120 insertions(+) diff --git a/src/basic/fileio.c b/src/basic/fileio.c index 90436f6ecf..66d06484dc 100644 --- a/src/basic/fileio.c +++ b/src/basic/fileio.c @@ -7,12 +7,15 @@ #include #include "alloc-util.h" +#include "chase.h" #include "errno-util.h" #include "extract-word.h" #include "fd-util.h" #include "fileio.h" #include "fs-util.h" #include "hexdecoct.h" +#include "io-util.h" +#include "iovec-util.h" #include "label.h" #include "log.h" #include "mkdir.h" @@ -1655,3 +1658,62 @@ int warn_file_is_world_accessible(const char *filename, struct stat *st, const c filename, st->st_mode & 07777); return 0; } + +int write_data_file_atomic_at( + int dir_fd, + const char *path, + const struct iovec *iovec, + WriteDataFileFlags flags) { + + int r; + + assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT)); + + /* This is a cousin of write_string_file_atomic(), but operates with arbitrary struct iovec binary + * data (rather than strings), works without FILE* streams, and does direct syscalls instead. */ + + _cleanup_free_ char *dn = NULL, *fn = NULL; + r = path_split_prefix_filename(path, &dn, &fn); + if (IN_SET(r, -EADDRNOTAVAIL, O_DIRECTORY)) + return -EISDIR; /* path refers to "." or "/" (which are dirs, which we cannot write), or is suffixed with "/" */ + if (r < 0) + return r; + + _cleanup_close_ int mfd = -EBADF; + if (dn) { + /* If there's a directory component, readjust our position */ + r = chaseat(dir_fd, + dn, + FLAGS_SET(flags, WRITE_DATA_FILE_MKDIR_0755) ? CHASE_MKDIR_0755 : 0, + /* ret_path= */ NULL, + &mfd); + if (r < 0) + return r; + + dir_fd = mfd; + } + + _cleanup_free_ char *t = NULL; + _cleanup_close_ int fd = open_tmpfile_linkable_at(dir_fd, fn, O_WRONLY|O_CLOEXEC, &t); + if (fd < 0) + return fd; + + CLEANUP_TMPFILE_AT(dir_fd, t); + + if (iovec_is_set(iovec)) { + r = loop_write(fd, iovec->iov_base, iovec->iov_len); + if (r < 0) + return r; + } + + r = fchmod_umask(fd, 0644); + if (r < 0) + return r; + + r = link_tmpfile_at(fd, dir_fd, t, fn, LINK_TMPFILE_REPLACE); + if (r < 0) + return r; + + t = mfree(t); /* disarm CLEANUP_TMPFILE_AT */ + return 0; +} diff --git a/src/basic/fileio.h b/src/basic/fileio.h index 578c16c0ee..3e2372c4dd 100644 --- a/src/basic/fileio.h +++ b/src/basic/fileio.h @@ -163,3 +163,9 @@ int safe_fgetc(FILE *f, char *ret); int warn_file_is_world_accessible(const char *filename, struct stat *st, const char *unit, unsigned line); int fopen_mode_to_flags(const char *mode); + +typedef enum WriteDataFileFlags { + WRITE_DATA_FILE_MKDIR_0755 = 1 << 0, +} WriteDataFileFlags; + +int write_data_file_atomic_at(int dir_fd, const char *path, const struct iovec *iovec, WriteDataFileFlags flags); diff --git a/src/test/test-fileio.c b/src/test/test-fileio.c index 38d9229946..575e2c52ed 100644 --- a/src/test/test-fileio.c +++ b/src/test/test-fileio.c @@ -9,6 +9,7 @@ #include "fd-util.h" #include "fileio.h" #include "fs-util.h" +#include "iovec-util.h" #include "memfd-util.h" #include "parse-util.h" #include "path-util.h" @@ -695,4 +696,55 @@ TEST(fdopen_independent) { f = safe_fclose(f); } +TEST(write_data_file_atomic_at) { + struct iovec a = IOVEC_MAKE_STRING("hallo"); + ASSERT_OK(write_data_file_atomic_at(AT_FDCWD, "/tmp/wdfa", &a, /* flags= */ 0)); + + _cleanup_(iovec_done) struct iovec ra = {}; + ASSERT_OK(read_full_file("/tmp/wdfa", (char**) &ra.iov_base, &ra.iov_len)); + ASSERT_EQ(iovec_memcmp(&a, &ra), 0); + ASSERT_OK_ERRNO(unlink("/tmp/wdfa")); + + ASSERT_OK(write_data_file_atomic_at(XAT_FDROOT, "tmp/wdfa", &a, /* flags= */ 0)); + iovec_done(&ra); + ASSERT_OK(read_full_file("/tmp/wdfa", (char**) &ra.iov_base, &ra.iov_len)); + ASSERT_EQ(iovec_memcmp(&a, &ra), 0); + ASSERT_OK_ERRNO(unlink("/tmp/wdfa")); + + ASSERT_ERROR(write_data_file_atomic_at(AT_FDCWD, NULL, &a, /* flags= */ 0), EINVAL); + ASSERT_ERROR(write_data_file_atomic_at(AT_FDCWD, "", &a, /* flags= */ 0), EINVAL); + ASSERT_ERROR(write_data_file_atomic_at(AT_FDCWD, "/", &a, /* flags= */ 0), EISDIR); + ASSERT_ERROR(write_data_file_atomic_at(AT_FDCWD, ".", &a, /* flags= */ 0), EISDIR); + ASSERT_ERROR(write_data_file_atomic_at(AT_FDCWD, "/tmp/", &a, /* flags= */ 0), EISDIR); + + _cleanup_free_ char *cwd = NULL; + ASSERT_OK(safe_getcwd(&cwd)); + ASSERT_OK_ERRNO(chdir("/tmp")); + + ASSERT_OK(write_data_file_atomic_at(AT_FDCWD, "wdfa", &a, /* flags= */ 0)); + iovec_done(&ra); + ASSERT_OK(read_full_file("/tmp/wdfa", (char**) &ra.iov_base, &ra.iov_len)); + ASSERT_EQ(iovec_memcmp(&a, &ra), 0); + ASSERT_OK_ERRNO(unlink("/tmp/wdfa")); + + ASSERT_OK(write_data_file_atomic_at(XAT_FDROOT, "tmp/wdfa", &a, /* flags= */ 0)); + iovec_done(&ra); + ASSERT_OK(read_full_file("/tmp/wdfa", (char**) &ra.iov_base, &ra.iov_len)); + ASSERT_EQ(iovec_memcmp(&a, &ra), 0); + ASSERT_OK_ERRNO(unlink("/tmp/wdfa")); + + ASSERT_OK_ERRNO(chdir(cwd)); + + ASSERT_ERROR(write_data_file_atomic_at(XAT_FDROOT, "tmp/zzz/wdfa", &a, /* flags= */ 0), ENOENT); + ASSERT_OK(write_data_file_atomic_at(XAT_FDROOT, "tmp/zzz/wdfa", &a, WRITE_DATA_FILE_MKDIR_0755)); + iovec_done(&ra); + ASSERT_OK(read_full_file("/tmp/zzz/wdfa", (char**) &ra.iov_base, &ra.iov_len)); + ASSERT_EQ(iovec_memcmp(&a, &ra), 0); + ASSERT_OK_ERRNO(unlink("/tmp/zzz/wdfa")); + + ASSERT_ERROR(write_data_file_atomic_at(AT_FDCWD, "/tmp/zzz", &a, /* flags= */ 0), EEXIST); + + ASSERT_OK_ERRNO(rmdir("/tmp/zzz")); +} + DEFINE_TEST_MAIN(LOG_DEBUG);