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fileio: introduce new mode to suppress writing the same value

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This commit is contained in:
Antony Deepak Thomas
2021-09-29 13:06:25 +09:00
committed by Yu Watanabe
parent 8034b42ca6
commit e565cfd2eb
2 changed files with 39 additions and 13 deletions
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src/basic/fileio.c
+27 -2
View File
@@ -148,6 +148,30 @@ int write_string_stream_ts(
return -EBADF;
}
if (flags & WRITE_STRING_FILE_SUPPRESS_REDUNDANT_VIRTUAL) {
_cleanup_free_ char *t = NULL;
/* If value to be written is same as that of the existing value, then suppress the write. */
if (fd < 0) {
fd = fileno(f);
if (fd < 0)
return -EBADF;
}
/* Read an additional byte to detect cases where the prefix matches but the rest
* doesn't. Also, 0 returned by read_virtual_file_fd() means the read was truncated and
* it won't be equal to the new value. */
if (read_virtual_file_fd(fd, strlen(line)+1, &t, NULL) > 0 &&
streq_skip_trailing_chars(line, t, NEWLINE)) {
log_debug("No change in value '%s', supressing write", line);
return 0;
}
if (lseek(fd, 0, SEEK_SET) < 0)
return -errno;
}
needs_nl = !(flags & WRITE_STRING_FILE_AVOID_NEWLINE) && !endswith(line, "\n");
if (needs_nl && (flags & WRITE_STRING_FILE_DISABLE_BUFFER)) {
@@ -263,10 +287,11 @@ int write_string_file_ts(
assert(!ts);
/* We manually build our own version of fopen(..., "we") that works without O_CREAT and with O_NOFOLLOW if needed. */
fd = open(fn, O_WRONLY|O_CLOEXEC|O_NOCTTY |
fd = open(fn, O_CLOEXEC|O_NOCTTY |
(FLAGS_SET(flags, WRITE_STRING_FILE_NOFOLLOW) ? O_NOFOLLOW : 0) |
(FLAGS_SET(flags, WRITE_STRING_FILE_CREATE) ? O_CREAT : 0) |
(FLAGS_SET(flags, WRITE_STRING_FILE_TRUNCATE) ? O_TRUNC : 0),
(FLAGS_SET(flags, WRITE_STRING_FILE_TRUNCATE) ? O_TRUNC : 0) |
(FLAGS_SET(flags, WRITE_STRING_FILE_SUPPRESS_REDUNDANT_VIRTUAL) ? O_RDWR : O_WRONLY),
(FLAGS_SET(flags, WRITE_STRING_FILE_MODE_0600) ? 0600 : 0666));
if (fd < 0) {
r = -errno;
src/basic/fileio.h
+12 -11
View File
@@ -15,17 +15,18 @@
#define LONG_LINE_MAX (1U*1024U*1024U)
typedef enum {
WRITE_STRING_FILE_CREATE = 1 << 0,
WRITE_STRING_FILE_TRUNCATE = 1 << 1,
WRITE_STRING_FILE_ATOMIC = 1 << 2,
WRITE_STRING_FILE_AVOID_NEWLINE = 1 << 3,
WRITE_STRING_FILE_VERIFY_ON_FAILURE = 1 << 4,
WRITE_STRING_FILE_VERIFY_IGNORE_NEWLINE = 1 << 5,
WRITE_STRING_FILE_SYNC = 1 << 6,
WRITE_STRING_FILE_DISABLE_BUFFER = 1 << 7,
WRITE_STRING_FILE_NOFOLLOW = 1 << 8,
WRITE_STRING_FILE_MKDIR_0755 = 1 << 9,
WRITE_STRING_FILE_MODE_0600 = 1 << 10,
WRITE_STRING_FILE_CREATE = 1 << 0,
WRITE_STRING_FILE_TRUNCATE = 1 << 1,
WRITE_STRING_FILE_ATOMIC = 1 << 2,
WRITE_STRING_FILE_AVOID_NEWLINE = 1 << 3,
WRITE_STRING_FILE_VERIFY_ON_FAILURE = 1 << 4,
WRITE_STRING_FILE_VERIFY_IGNORE_NEWLINE = 1 << 5,
WRITE_STRING_FILE_SYNC = 1 << 6,
WRITE_STRING_FILE_DISABLE_BUFFER = 1 << 7,
WRITE_STRING_FILE_NOFOLLOW = 1 << 8,
WRITE_STRING_FILE_MKDIR_0755 = 1 << 9,
WRITE_STRING_FILE_MODE_0600 = 1 << 10,
WRITE_STRING_FILE_SUPPRESS_REDUNDANT_VIRTUAL = 1 << 11,
/* And before you wonder, why write_string_file_atomic_label_ts() is a separate function instead of just one
more flag here: it's about linking: we don't want to pull -lselinux into all users of write_string_file()