The system has an MMC with FAT partition. The FAT partition contains some files, two of them are called "file_A" and "file_B".
I need to prepare a script to toggle between file_A and file_B at the u-boot stage without knowing the file's size in advance.
I thought to use fatload and fatwrite commands.
I loaded the file to the RAM using fatload without issues using:
fatload mmc 0:1 0x0 file_A
Now I have issues with copying the file residing in the RAM to the fat partition using fatwrite, again I don't now the file size in advance (I've noticed that the fatload print information contains the file size, maybe I can use it somehow?).
Most commands to load something in to memory set the filesize variable to how much was loaded in to memory.
Related
I am working on a final project for school that involves making a program that reads and writes to files on persistent memory. I don't have access to an actual persistent memory device so I followed the tutorial at the following link to emulate it:
https://kb.pmem.io/howto/100000012-How-To-Emulate-Persistent-Memory-using-the-Linux-memmapKernel-Option/
user#node:~/test2$ sudo fdisk -l /dev/pmem0
Disk /dev/pmem0: 8 GiB, 8589934592 bytes, 16777216 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes
According to the above output, I have an emulated persistent memory partition on my dram hard drive named pmem0. I used the tutorial at the following link to get some sample code on how to read and write from files on persistent memory:
https://www.intel.com/content/www/us/en/developer/articles/code-sample/create-a-persistent-memory-hello-world-program-using-libpmemobj-with-c.html
I compile and run the code and the output of the program says it is writing a file to persistent memory. I wanted to check if the file is being written to the correct partition so I used the command:
df -P fileName | tail -1 | cut -d' ' -f 1 (which I got from another stackoverflow post) and the output is /dev/sda1 when I believe it should be /dev/pmem0 if it is actually using the persistent memory partition.
I'm looking for tips on how to ensure I am actually mapping my code to the persistent memory partition I created.
The code from the second link needs to have the pmdk library setup to run properly and I needed to modify my linux kernel boot parameters to setup the partition so I'm not sure if I can supply a much better minimal example.
Edit: I believe the exact lines of code I need to modify would be one of:
pop = pmemobj_create(path, LAYOUT, PMEMOBJ_MIN_POOL, 0666);
PMEMoid root = pmemobj_root(pop, sizeof (struct my_root));
pmemobj_persist(pop, &rootp->len, sizeof (rootp->len));`
This creates the persistent memory pool but the tutorial doesn't seem to mention how to actually map to a persistent memory device.
why does the string get written to the hard drive in sda1, which I believe is regular memory?
The referred C program calls pmemobj_create() with the path you specify as the second program argument, in your case fileName. If the current working directory is on the hard drive, the created memory pool file fileName is of course also residing on the hard drive. If you want a file to be created on your /dev/pmem0 disk, you have to mount that file system and use a path to a file thereon.
When a file is saved into a drive, its contents are written & then indexed. I want to get the indexes and to access the raw contents of the files.
Any idea on the method how to do it, especially for ex4 & btrfs?
UPDATE: I want to get the addresses of the extents of a file. The information about the addresses must be stored somewhere onto the disk. I want to retrieve this info, in order to map the physical location of the file contents. Any methods in order to achieve that?
UPDATE: Hello, all! Thanks for your replies. What I want is a function/command which returns me a list of extent addresses. debugfs seems the function/command with the most-relevant functionality.
It depends of the filesystem you are using. If you are running Linux you can use debufs to seek the file in the filesystem.
I have to say that all FSs are mounted through a VFS, a virtual filesystem that is like a simplified interface with the standard operations (open, close, read...). What is the meaning of that? No filesystem nor its contents(files, dirs) are opened directly from disk, when you open something, you move it to the main memory(your RAM) you do your operations and when you close something it returns to the disk drive.
Now, the question is: Can I get the absolute address in a FS? Yes, if you open your whole filesystem like open ("/dev/sdaX", 0_RDONLY); so you get the address relative to your filesystem using lseek in C for example.
And then... Can I get the same in the whole drive? No, that is because you cannot open the whole drive as a file descriptor. Remember /dev/sdaXin UNIX? Partitions and its can be opened like files because they have a virtual interface running on them.
Your last answer: Can I read really raw contents? All files are read as they appear on disk, the only thing that changes is the descriptor used by the OS and some data about how is indexed, all this as a "file header".
I hope all your questions are answered.
The current solution/workaround is to call these functions with popen:
filefrag -e /path/to/file
hdparm --fibmap /path/to/filename
Then one should simply parse the stringoutputs of these programs. It is not a real solution (i.e.: outputs at C/C++ level), but I'll accept it for now.
Sources:
https://unix.stackexchange.com/questions/106802/what-command-do-i-use-to-see-the-start-and-end-block-of-a-file-in-the-file-syste
https://serverfault.com/questions/29886/how-do-i-list-a-files-data-blocks-on-linux
In my program there is a function to frequently call stat() to get the attributes of a file in flash storage. Sometimes after power off and reboot the contents of the file lost. I noticed that the stat() finally calls the file system driver in the Linux kernel.
My questions are: will the Linux kernel fs open or read the file to get the file attributes? Is it possible for the power off during stat() or fstat() corrupt the file in flash?
All the stat() call does is to retrieve the contents of the file's i-node; the file itself isn't touched. However, the file's i-node will be in memory, and it the file was updated in any way [even by being held open by this or another process], the file mtime and such will need to be updated and the i-node will get updated, perhaps wrongly. Poof! No file.
But this behavior is not unique to flash.
I need to clear sector 0 for removable media devices (custom USB memory devices) which I have been trying to clear within a WPF/C# application. My first attempt was to use DD, but I ran into problems. During the manufacturing of the devices a MBR is created at sector 0 and the volume (logical?) starts at sector 40. When I issue the following command it clears sector 40 and not sector 0:
dd bs=512 count=1 if=/dev/zero of=\.\E:
I found another version of DD here which includes a wipe utility. I tried this version and I am seeing the same behavior. I am using both HxD and Runtime's DiskExplorer that sector 40 is being cleared and not sector 0. I could use HxD or Runtime's DiskExplorer, but this needs to be scriptable.
Does anyone know of any other methods of clearing (filling) sector 0 within Windows XP SP2?? Any help would be greatly appreciated. Thanks.
Mark
Solution: My solution used WMI to find the physical drive based upon the logical drive letter. First, query the Win32_LogicalDiskToPartition class to find the logical drive I am looking for. This provides the Antecedent field which constains something like '...DeviceID="Disk #X, Partition #Y"'. Next, I query Win32_DiskDriveToDiskPartition class while searching against the Dependent field to find the match for the Antecedent field within the Win32_LogicalDiskToPartition class. Once found, the Antecedent field from Win32_LogicalDiskToPartition will yield the physical drive. I selected atzz since it is the closes to my solution. I wanted to use Eugene's suggestion, but I only had a few hours to implement this so I selected the easier of the two. I will need to revisit this at a later time though.
There are two ways to format a USB drive, from Windows standpoint:
As a floppy disk. In this case entire USB drive contains a single file system, and its boot record is located in sector 0.
As a hard drive. In this case, sector 0 contains MBR with partition table. Actual file system(s) with their individual boot records are located further on the drive.
I think you are observing the second case. Using \.\E: to identify the device, you end up accessing file system's boot record instead of MBR.
Here is how you can access sector 0 of the USB drive.
Load WinObj from here.
In WinObj, under GLOBAL??, find E:. It will be a SymbolicLink pointing to something like \Device\Harddisk2\DP(1)0-0+30.
Under GLOBAL??, find a PhysicalDrive# symlink referring to the same Harddisk# that you found on step 2. Most probably it will have the same numeric suffix as Harddisk#. E.g.: SymbolicLink PhysicalDrive2 refers to \Device\Harddisk2\DR47.
Use the PhysicalDrive# you've found in DD command:
dd bs=512 count=1 if=\\.\PhysicalDrive2 of=mbr.dat
You are trying to clear logical device E: and not physical device. Try doing the following:
call CreateFile() WinAPI function to open "\\.\PhysicalDriveX" where X is the number of the device (see Remarks in description of CreateFile function for information about how to open the physical device properly). Then use WriteFile API function to write 512 bytes at offset 0 of the opened device.
If you get permission denied error when opening the device for writing, you can take our RawDisk product (trial version will work fine for you) which lets one bypass this security measure of Windows.
upd: As for calling CreateFile from C#, see PInvoke.net.
Is there a way to determine if a USB drive has been formatted as FAT, FAT32 or NTFS?
I think you can plug it into a Linux box and figure out what is the device (dmesg), then something like fdisk -l [device] will print out the partitions and their types.
use "mount" to show all mounted file systems. It shows the file system type and mount parameters.