Every time my function is getting called it is overwriting to the file. Kindly note I am opening file in unbuffered mode using below flags.
FILE_FLAG_NO_BUFFERING | FILE_FLAG_WRITE_THROUGH
If I am using simple buffered mode it is working fine.
FILE_ATTRIBUTE_NORMAL
I am getting following error in unbuffered mode.
** ERROR ** CreateFile failed: The parameter is incorrect.
Kindly find the code snippets below. This piece of code getting called many times.
HANDLE hFile;
LPCWSTR file_path = convertCharArrayToLPCWSTR(UNBUFFERED_FILE);
hFile = CreateFile(file_path,
FILE_APPEND_DATA,
FILE_SHARE_WRITE,
NULL,
OPEN_ALWAYS,
FILE_FLAG_NO_BUFFERING | FILE_FLAG_WRITE_THROUGH,
NULL
);
if (hFile == INVALID_HANDLE_VALUE)
{
std::cout << "Unable to open/create file for writing" << std::endl;
PrintError(TEXT("CreateFile failed"));
}
Data *data = new Data();
DWORD dwBytesToWrite = sizeof(Data);
DWORD dwBytesWritten = 0;
BOOL bErrorFlag = FALSE;
bErrorFlag = WriteFile(
hFile, // open file handle
data, // start of data to write
dwBytesToWrite, // number of bytes to write
&dwBytesWritten, // number of bytes that were written
NULL);
if (bErrorFlag == FALSE)
{
std::cout << "Unable to write to file" << std::endl;
PrintError(TEXT("Unable to write to file"));
}
if (dwBytesToWrite != dwBytesWritten)
{
std::cout << "Error in writing: Whole data not written" << std::endl;
PrintError(TEXT("Error in writing: Whole data not written"));
}
CloseHandle(hFile);
.
Kindly suggest if any alternative idea is available.
from NtCreateFile
FILE_NO_INTERMEDIATE_BUFFERING
The file cannot be cached or buffered in a driver's internal
buffers. This flag is incompatible with the DesiredAccess
parameter's FILE_APPEND_DATA flag.
so when you call
CreateFile(file_path,
FILE_APPEND_DATA, // !!
FILE_SHARE_WRITE,
NULL,
OPEN_ALWAYS,
FILE_FLAG_NO_BUFFERING /*!!*/| FILE_FLAG_WRITE_THROUGH,
NULL
);
you use FILE_FLAG_NO_BUFFERING (mapped to FILE_NO_INTERMEDIATE_BUFFERING) with FILE_APPEND_DATA - you and must got ERROR_INVALID_PARAMETER. you need remove one flag. i suggest remove FILE_FLAG_NO_BUFFERING flag, because with it you can write only integral of the sector size.
Related
Given one normal file, it could be read and written. Then I change this file attribute to Read-only through
However, this file still could be written through file handler. Here are my codes
#define CREATE_FILE_OPT FILE_ATTRIBUTE_NORMAL | FILE_FLAG_WRITE_THROUGH | FILE_FLAG_RANDOM_ACCESS
std::string name("test.txt");
HANDLE hfile = ::CreateFile(name.c_str(),
GENERIC_READ | GENERIC_WRITE, NULL, NULL, OPEN_EXISTING, CREATE_FILE_OPT, NULL);
if (hfile == INVALID_HANDLE_VALUE) {
hfile = ::CreateFile(name.c_str(),
GENERIC_READ | GENERIC_WRITE, NULL, NULL, CREATE_NEW, CREATE_FILE_OPT, NULL);
if (hfile == INVALID_HANDLE_VALUE) {
printf("so sad, invalid file handler....");
return -1;
}
}
int i = 0;
char rbuf[] = "you are";
DWORD bytesWritten;
do {
Sleep(5000);
++i;
bytesWritten = 0;
BOOL bret = ::WriteFile(hfile, rbuf, strlen(rbuf), &bytesWritten, NULL);
if (bret == FALSE) {
printf("Cannot write bytes into file.....");
DWORD err = GetLastError();
printf("The error code is %d\n", err);
}
else
printf("write %d bytes to file\n", bytesWritten);
DWORD ret = GetFileAttributes(name.c_str());
printf("The file attribute is %d\n", ret);
} while (i < 10000);
The file attribute is 32 before I change it to Read-only, but it will be 33 after this file is Read-only.
I want to know why the file could be written after change it to Read-only? Is there any issue in my test codes?
PS: test it in VS2015 under windows 7.
Sorry, I get your meaning finally. I guess you are talking about creating a file first, setting it readonly without closing the program. The READONLY attribute check only happens in CreateFile routine.
In Windows kernel, every object is assigned a temporary access right list once created, unless explicitly refreshed, a thing seldom happens on actual files on fixed disks. So even if you deny all rights after CreateFile using NTFS access control, your program will behave just as when CreateFile is called.
In conclusion, it is natural your program can still write to the file, after your hot-changing it into READONLY, which only writes information onto disk, not changing kernel access table.
Here's my code in which I've got on an infinite loop (to my knowledge)
while(true) {
DWORD TitleID = XamGetCurrentTitleId();
std::ostringstream titleMessageSS;
titleMessageSS << "Here's the current title we're on : " << TitleID << "\n\n";
std::string titleMessage = titleMessageSS.str(); // get the string from the stream
DWORD dwBytesToWrite = (DWORD)titleMessage.size();
DWORD dwBytesWritten = 0;
BOOL bErrorFlag = FALSE;
HANDLE logFile = CreateFile( "Hdd:\\LOGFile.txt", GENERIC_WRITE, 0, NULL, CREATE_NEW, FILE_ATTRIBUTE_NORMAL, NULL);
bErrorFlag = WriteFile(logFile, titleMessage.c_str(), dwBytesToWrite, &dwBytesWritten, NULL);
CloseHandle(logFile);
Sleep(30000);
}
return NULL;
Does anyone see a reason as to why this only writes just once? I've waited over 5 minutes to see if it does anything in the end to no avail.
The Flag CREATE_NEW in CreateFile prevents the update of the file because CreateFile fail with ERROR_FILE_EXISTS. Use OPEN_ALWAYS instead.
Also it will always truncate. Replace GENERIC_WRITE with FILE_APPEND_DATA if you want to add a new line at the end of your logfile.
The whole CreateFile line should be:
HANDLE logFile = CreateFile( "Hdd:\\LOGFile.txt", FILE_APPEND_DATA , 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
Read CreateFile documentation carefully, it worth it, because it has a central role in the windows IO universe:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858(v=vs.85).aspx
look also add:
https://stackoverflow.com/a/9891875/1922748
As Martin James mentioned, from MSDN:
CREATE_NEW
Creates a new file, only if it does not already exist.
If the specified file exists, the function fails and the last-error
code is set to ERROR_FILE_EXISTS (80).
If the specified file does not exist and is a valid path to a writable
location, a new file is created.
So it seems that the handle is invalid after the first call, and hence WriteFile() fails.
I have locked a file using LockFileEx, but I am not able to open a stream from it.
HANDLE indexHandle = CreateFile (indexFileName, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, 0,
OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);
bool indexLock = false;
OVERLAPPED overlapped;
memset (&overlapped, 0, sizeof (overlapped));
while (noOfTries >0 && !indexLock)
{
if (!LockFileEx (indexHandle, LOCKFILE_EXCLUSIVE_LOCK, 0, 0, UINT_MAX, &overlapped))
{
InfoLog << "Failed to get lock on index file -- Error code is ["
<< GetLastError () <<"]"<<std::endl;
Sleep(sleepTime);
noOfTries--;
}
else
{
indexLock=true;
}
}
After the lock is acquired, I want to do this:
string indexFile = mPath + Util::PATH_SEPARATOR + mIndexFileName;
os.open( indexFile.c_str(), ios_base::app);
if (!os)
{
InfoLog << "BinaryFileSystemObjectStore:: ofstream: Failed to open index for write: " << indexFile.c_str() << endl;
}
I do this because I find it easier to read line by line with streams...
Is there a solution?
From the documentation for LockFileEx:
If the locking process opens the file a second time, it cannot access the specified region through this second handle until it unlocks the region.
So you need to use the handle you already have rather than creating a new one.
The _open_osfhandle function allows you to create a file descriptor from an existing handle, and you can then pass this file descriptor to the ofstream constructor instead of the filename.
You open the file with FILE_SHARE_READ. This means you permit further opening of the file for reading only. Then you try to open it for writing, which will fail.
Use FILE_SHARE_READ | FILE_SHARE_WRITE instead.
Everytime this function is called the old text data is lost?? Tell me how to maintain previous data and appending new data.
This function is called 10 times:
void WriteEvent(LPWSTR pRenderedContent)
{
HANDLE hFile;
DWORD dwBytesToWrite = ((DWORD)wcslen(pRenderedContent)*2);
DWORD dwBytesWritten = 0;
BOOL bErrorFlag = FALSE;
printf("\n");
hFile = CreateFile(L"D:\\EventsLog.txt", FILE_ALL_ACCESS, 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile == INVALID_HANDLE_VALUE)
{
printf("Terminal failure: Unable to open file \"EventsLog.txt\" for write.\n");
return;
}
printf("Writing %d bytes to EventsLog.txt.\n", dwBytesToWrite);
bErrorFlag = WriteFile(
hFile, // open file handle
pRenderedContent, // start of data to write
dwBytesToWrite, // number of bytes to write
&dwBytesWritten, // number of bytes that were written
NULL); // no overlapped structure
if (FALSE == bErrorFlag)
{
printf("Terminal failure: Unable to write to file.\n");
}
else
{
if (dwBytesWritten != dwBytesToWrite)
{
printf("Error: dwBytesWritten != dwBytesToWrite\n");
}
else
{
printf("Wrote %d bytes to EventsLog.txt successfully.\n",dwBytesWritten);
}
}
CloseHandle(hFile);
}
You should pass FILE_APPEND_DATA as the dwDesiredAccess to CreateFile, as documented under File Access Rights Constants (see sample code at Appending One File to Another File). While this opens the file using the correct access rights, your code is still responsible for setting the file pointer. This is necessary, because:
Each time a file is opened, the system places the file pointer at the beginning of the file, which is offset zero.
The file pointer can be set using the SetFilePointer API after opening the file:
hFile = CreateFile( L"D:\\EventsLog.txt", FILE_APPEND_DATA, 0x0, nullptr,
OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr );
if ( hFile == INVALID_HANDLE_VALUE ) {
printf( "Terminal failure: Unable to open file \"EventsLog.txt\" for write.\n" );
return;
}
// Set the file pointer to the end-of-file:
DWORD dwMoved = ::SetFilePointer( hFile, 0l, nullptr, FILE_END );
if ( dwMoved == INVALID_SET_FILE_POINTER ) {
printf( "Terminal failure: Unable to set file pointer to end-of-file.\n" );
return;
}
printf("Writing %d bytes to EventsLog.txt.\n", dwBytesToWrite);
bErrorFlag = WriteFile( // ...
Unrelated to your question, the calculation of dwBytesToWrite should not use magic numbers. Instead of * 2 you should probably write * sizeof(*pRenderedContent). The parameter to WriteEvent should be constant as well:
WriteEvent(LPCWSTR pRenderedContent)
The parameter for appending data to a file is FILE_APPEND_DATA instead of FILE_ALL_ACCESS in the CreateFile function.
Here is an example: http://msdn.microsoft.com/en-us/library/windows/desktop/aa363778(v=vs.85).aspx
Anyone out there have experience of c/c++ IOCTL calls?
Basically I'm trying to identify what port a USB memory stick is plugged into.
I have all the USB info and have volume info. Apparantly to link these 2 blocks of info I need either the driver-key or serial-number.
However when calling DeviceIoControl I'm getting invalid handle as the "last error code"
My drive USB drive mounted to a directory in c:\ (not a drive letter) See below
//get a handle on the volume
HANDLE hVolume;
DWORD dwAccessFlags;
dwAccessFlags = GENERIC_READ | GENERIC_WRITE;
hVolume = CreateFile(L"C:\_USB\MP1",
dwAccessFlags,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
0,
NULL );
if (hVolume == INVALID_HANDLE_VALUE) {
printf("Invalid Handle");
}
//use the handle
MEDIA_SERIAL_NUMBER_DATA* pserialNumberData = new MEDIA_SERIAL_NUMBER_DATA;
wstring result;
//HANDLE hVolume = OpenVolume(vname.substr(0, vname.length() - 1).c_str());
DWORD bytesReturned = 0;
LPDWORD lpBytesReturned = &bytesReturned;
OVERLAPPED over;
LPOVERLAPPED lpOver = &over;
BOOL success = 1;
success = DeviceIoControl(
(HANDLE) hVolume, // handle to device
IOCTL_STORAGE_GET_MEDIA_SERIAL_NUMBER, // dwIoControlCode
NULL, // lpInBuffer
0, // nInBufferSize
(LPVOID) pserialNumberData, // output buffer
(DWORD) sizeof(MEDIA_SERIAL_NUMBER_DATA), // size of output buffer
(LPDWORD) lpBytesReturned, // number of bytes returned
(LPOVERLAPPED) lpOver // OVERLAPPED structure
);
wcout << L"--> GetSn() DeviceIoControl success " << success << endl;
wcout << L"--> GetSn() DeviceIoControl Last error number " << GetLastError() << endl;
wcout << L"--> GetSn() DeviceIoControl Bytes Returned " << bytesReturned << endl;
wcout << L"--> GetSn() DeviceIoControl struct size " << sizeof(MEDIA_SERIAL_NUMBER_DATA) << endl;
If you look at the Remarks section for the DeviceIoControl function, it says:
To retrieve a handle to the device, you must call the CreateFile function with either the name of a device or the name of the driver associated with a device. To specify a device name, use the following format:
\\.\DeviceName
DeviceIoControl can accept a handle to a specific device. For example, to open a handle to the logical drive A: with CreateFile, specify \\.\a:. Alternatively, you can use the names \\.\PhysicalDrive0, \\.\PhysicalDrive1, and so on, to open handles to the physical drives on a system.
You are not opening a device handle, and thus DeviceIoControl is not going to work for that case.
The first big problem I see is that the CreateFile function must be called with the FILE_FLAG_BACKUP_SEMANTICS flag in order to get a valid handle to a directory. So, for starters, try:
hVolume = CreateFile( L"C:\_USB\MP1",
dwAccessFlags,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS,
NULL );
Hmmm... I think the handle you get from CreateFile is the handle to the directory you mounted your drive to, rather than the drive itself. To be sure you get the handle to device you want, you should use a device path, e.g. \\.\Device\HarddiskVolume1. WinObj or DeviceTree can probably help you find the path to your usb drive.