Reading a USB device

[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