Reading a USB device

koumodaki

Hi, I have been trying to read a file in a program from a USB flash drive. I know that windows allows me to use the device as a drive and I can read the file like reading from any other drive. But the problem is the flash drive will be connected to different PC and the drive name could change. So I cannot use the drive name. I am using SetupDI API to get the interface and I am also able to get the handle using CreateFile(). But I do not know how to read a particular file. Can anyone help me here? Also is there any tutorial that will help me to work with USB drives in WinXP environment?

David Crow

koumodaki wrote:

But I do not know how to read a particular file.

Do you know the file's name?

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

koumodaki

Yes I do know the file's name.

David Crow

So then can't you call ReadFile()?

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

koumodaki

I have a file context.cfg which needs to be read form the flash drive. How do I specify in the ReadFile() parameters that I need to read this particular file. From what I know, I can pass the handle I obtain while opening the usb flash drive from CreateFile() to this function. How do I get hold of the file inside the flash drive

David Crow

What does your call to CreateFile() look like?

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

koumodaki

I enumarate the USB device first and get the interface using SetupDiGetDeviceInterfaceDetail(). The name is stored in a vector Devices. Then I use the following call: HANDLE hUsbDevice = CreateFile(Devices[0].c_str(), GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);

David Crow

So what happens if you use:

string str = Devices[0] + "\\context.cfg";
HANDLE hUsbDevice = CreateFile(str.c_str(), GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

koumodaki

Havent tried that. Will check it out

JudyL_MD

koumodaki wrote:

I can pass the handle I obtain while opening the usb flash drive from CreateFile() to this function.

The problem is that this handle is a handle to the physical drive. You can't use that to easily find a file on the drive. Your basic problem is how to convert from a USB identifier to the logical hard drive letter. Using WMI you can go from something like USBSTOR\\DISK&VEN_SANDISK&PROD_CRUZER_MINI&REV_0.1\\20041100801E102869&0 (to take an example not at random) to G:. Stick the USB flash in your system, fire up the WMI object browser and you can see the queries you need to make to WMI to go from the former to the latter. Judy

koumodaki

I tried the method you suggested. I did not work. The code snippet is std::string path = Devices[0] + "\\context.cfg"; HANDLE hUsbDevice = CreateFile(Devices[0].c_str(), GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL); if (hUsbDevice == INVALID_HANDLE_VALUE) return 1; char data[MAX_PATH]; DWORD nNumberOfBytesToRead = MAX_PATH; DWORD lpNumberOfBytesRead = 0; if(!ReadFile(hUsbDevice,(void*)data, nNumberOfBytesToRead, &lpNumberOfBytesRead,NULL)) { int err = GetLastError(); return 0; } GetLastError() returns ERROR_INVALID_PARAMETER

David Crow

koumodaki wrote:

I tried the method you suggested.

But the code snippet you posted does not reflect such. You are not using path. I like Judy's suggestion better.

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

koumodaki

I used the path but made a mistake while copying the code here. Ok so maybe I will try using WMI. Do you have any tutorial which explains how to use Windows API in such situatuons?

koumodaki

Thanks Judy. I will try this

David Crow

JudyL_FL wrote:

...fire up the WMI object browser and you can see the queries you need to make to WMI to go from the former to the latter.

Interesting tool. I inserted a PNY Attache drive and tried it. I found "E:" under the Win32_LogicalDisk node, and "USB\VID_154B&PID_0005\6E68190046F6" under the Win32_USBHub node. I then found "USBSTOR\DISK&VEN_PNY&PROD_USB_2.0_FD&REV_PMAP\6E68190046F6&0" under the Win32_DiskDrive node. Where are these queries to which you refer?

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

JudyL_MD

If you follow Win32_SystemDevices to Win32_PnPEntity, you should find a leaf with a device id something like USBSTOR..... From there, you can get (look under Win32_PnPDevice) the correct DeviceId to use for Win32_DiskDrive. From there, you can get (look under Win32_DiskDriveToDiskPartition) the correct DeviceId to use for Win32_DiskPartition. From there, you can get (look under Win32_LogicalDiskToPartition) the correct DeviceId to use for Win32_LogicalDisk. That final device id is the logical drive number. (Whew!! ) Getting that first USBSTOR... monster string is what's usually the hardest part of this sort of thing since you have to use the SetupDi API. That is truly nasty!! Judy

David Crow

Wow! I need an elevator to come back to the surface from drilling down that deep. It works, though.

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne