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authorAdrian Kummerlaender2016-02-20 22:30:11 +0100
committerAdrian Kummerlaender2016-02-20 22:30:11 +0100
commitb3ef0fc8daa41e433f1919a4933a1cc047f59341 (patch)
treeb551c34e381d6df29334848d6aff242c14b69817
parentee51dc19c859e718280bebae1c089be058737b1c (diff)
Interpose `open` library function
`open` is not as side effect free as I had imagined - i.e. if the flag `O_TRUNC` is passed it truncates the file contents alongside opening the file descriptor. In practice this is done by _emacs_ prior to writing the new file content and as such needs to be intercepted so we can start tracking the file before it is changed. Interposing `open` required some changes to make the library work without including `fcntl.h`. This header not only defines some of the flags we require to check if a library call actually is able to change files but also defines the `open` library function. While implementing this change I noticed that the function interpositions implemented in C++ actually need to be declared as `external "C"` so their names do not get wrangled during compilation. I suspect that this was previously implicitly done for e.g. `mmap` and `write` by the included C standard library headers. However this did not work for `open` which is why all function interpositions are now explicitly declared external. End result: _emacs_ file changes are now tracked correctly.
-rw-r--r--README.md2
-rw-r--r--src/actual.h3
-rw-r--r--src/bootstrap.cc4
-rw-r--r--src/main.cc41
-rw-r--r--src/tracking/change_tracker.cc2
-rw-r--r--src/utility/logger.h3
6 files changed, 48 insertions, 7 deletions
diff --git a/README.md b/README.md
index e265747..4d155de 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,7 @@ The goal is to develop `change` into a utility that can be dropped in front of a
## Filtering
-Due to it's nature of interposing low level system calls such as `write` and `unlink` the library by default exposes lots of the internal write logic of the wrapped application. For instance it reports _vim_ creating a file called `4913` to verify the target directory's writability as well as the creation of various temporary backup files. While this is certainly interesting for debugging purposes it hinders the library's goal of providing a higher level summary consisting primarily of the actions the user explicity performed such as the changed file contents.
+Due to it's nature of interposing low level calls such as `write` and `unlink` the library by default exposes lots of the internal write logic of the wrapped application. For instance it reports _vim_ creating a file called `4913` to verify the target directory's writability as well as the creation of various temporary backup files. While this is certainly interesting for debugging purposes it hinders the library's goal of providing a higher level summary consisting primarily of the actions the user explicity performed such as the changed file contents.
To solve this problem one may provide a list of regular expressions to be matched against the file paths via the `CHANGE_LOG_IGNORE_PATTERN_PATH` environment variable.
diff --git a/src/actual.h b/src/actual.h
index a860590..ae951b9 100644
--- a/src/actual.h
+++ b/src/actual.h
@@ -6,9 +6,6 @@
#endif
#include <dlfcn.h>
-#include <sys/mman.h>
-#include <sys/uio.h>
-
#include <memory>
#include <cstring>
diff --git a/src/bootstrap.cc b/src/bootstrap.cc
index 309ff20..1d509d8 100644
--- a/src/bootstrap.cc
+++ b/src/bootstrap.cc
@@ -2,6 +2,8 @@
#include "init/alloc.h"
+extern "C" {
+
void free(void* ptr) {
static actual::ptr<void, void*> actual_free{};
@@ -41,3 +43,5 @@ void* calloc(size_t block, size_t size) {
return actual_calloc(block, size);
}
}
+
+}
diff --git a/src/main.cc b/src/main.cc
index 8b6ca23..7e849fd 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -1,3 +1,7 @@
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/uio.h>
+
#include "actual.h"
#include "utility/io.h"
@@ -61,6 +65,14 @@ inline void track_write(const int fd) {
}
}
+inline void track_write(const std::string& path) {
+ if ( enabled && utility::is_regular_file(path.c_str()) ) {
+ if ( !matcher->isMatching(path) ) {
+ tracker->track(path);
+ }
+ }
+}
+
inline void track_rename(
const std::string& old_path, const std::string& new_path) {
if ( enabled ) {
@@ -82,6 +94,28 @@ inline void track_remove(const std::string& path) {
}
}
+extern "C" {
+
+int open(const char* path, int flags, mode_t mode) {
+ static actual::ptr<int, const char*, int, mode_t> actual_open{};
+
+ if ( !actual_open ) {
+ actual_open = actual::get_ptr<decltype(actual_open)>("open");
+ }
+
+ // `open` may reset the file contents when used with the `O_TRUNC` flag.
+ // e.g. this is how _emacs_ clears the file content prior to writing the
+ // new content.
+ // Normally `O_TRUNC` is defined in `fcntl.h` which we can not include
+ // as it defines the very c-function we are currently _overriding_.
+ //
+ if ( flags & 01000 ) {
+ track_write(path);
+ }
+
+ return actual_open(path, flags, mode);
+}
+
ssize_t write(int fd, const void* buffer, size_t count) {
static actual::ptr<ssize_t, int, const void*, size_t> actual_write{};
@@ -163,7 +197,10 @@ int unlinkat(int dirfd, const char* path, int flags) {
actual_unlinkat = actual::get_ptr<decltype(actual_unlinkat)>("unlinkat");
}
- if ( dirfd == AT_FDCWD ) {
+ // Normally `AT_FDCWD` is defined in `fcntl.h` which we can not include
+ // as it defines `open` which this library also aims to override.
+ //
+ if ( dirfd == -100 ) {
track_remove(path);
} else {
track_remove(utility::get_file_path(dirfd) + path);
@@ -171,3 +208,5 @@ int unlinkat(int dirfd, const char* path, int flags) {
return actual_unlinkat(dirfd, path, flags);
}
+
+}
diff --git a/src/tracking/change_tracker.cc b/src/tracking/change_tracker.cc
index bc8465e..c966c04 100644
--- a/src/tracking/change_tracker.cc
+++ b/src/tracking/change_tracker.cc
@@ -1,7 +1,7 @@
#include "change_tracker.h"
+#include <boost/process.hpp>
#include <boost/filesystem.hpp>
-#include <boost/filesystem/fstream.hpp>
namespace {
diff --git a/src/utility/logger.h b/src/utility/logger.h
index 0dd88a6..229032c 100644
--- a/src/utility/logger.h
+++ b/src/utility/logger.h
@@ -5,7 +5,8 @@
#include <ext/stdio_filebuf.h>
-#include <boost/process.hpp>
+#include <boost/filesystem.hpp>
+#include <boost/process/pistream.hpp>
namespace utility {