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Top Forums Programming write() issue during a low level hdd access Post 302397288 by sponnusa on Sunday 21st of February 2010 06:10:44 PM
Old 02-21-2010
thank you.

So, there is no way around it without writing a device driver to handle the read/write operations? Is that right?

I have a utility written in python which able to identify the bad sectors exactly as the same way as the C program. I am not sure, if python would have implemented anything internally (a device driver) to achieve this. I'm currently downloading the python source code to analyse.

I am sure C is more low level then python (which is btw the dumbest statement, i've said Smilie) and should be able to achieve it. It's little weird that the program fails to identify the bad sectors. I have analysed the following programs so far for such an implementation. And all have the same code.

Testdisk, dd, ddrescue, badblocks etc.,.

So does this conclude that the none of the above available usermode linux opensource programs are really doing what they are claiming for? (data recovery / forensics utilities?) All the above program implements O_DIRECT options too.

Well, I guess I am in need of a fix now! Smilie

It also sounds a little weird that there are no user mode programs (not even one?) available in linux that can do a direct I/O with the disk. (Except that I am willing to write one using the libata / scsi libraries which can directly talk to the ATA (PATA / SATA) devices using ATA protocol (i've done this in dos using assembly) and SG / SCSI protocol to the scsi devices).

Anyways, thanks for all your input and guidance. Atleast it got me to do the O_DIRECT implementation. Please update this thread if there are any more information to be shared / assisted.

Thanks again for all the help. Smilie
 

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Tcl_Access(3)						      Tcl Library Procedures						     Tcl_Access(3)

__________________________________________________________________________________________________________________________________________________

NAME
Tcl_Access, Tcl_Stat - check file permissions and other attributes SYNOPSIS
#include <tcl.h> int Tcl_Access(path, mode) int Tcl_Stat(path, statPtr) ARGUMENTS
char *path (in) Native name of the file to check the attributes of. int mode (in) Mask consisting of one or more of R_OK, W_OK, X_OK and F_OK. R_OK, W_OK and X_OK request checking whether the file exists and has read, write and execute permissions, respectively. F_OK just requests checking for the existence of the file. struct stat *statPtr (out) The structure that contains the result. _________________________________________________________________ DESCRIPTION
As of Tcl 8.4, the object-based APIs Tcl_FSAccess and Tcl_FSStat should be used in preference to Tcl_Access and Tcl_Stat, wherever possi- ble. There are two reasons for calling Tcl_Access and Tcl_Stat rather than calling system level functions access and stat directly. First, the Windows implementation of both functions fixes some bugs in the system level calls. Second, both Tcl_Access and Tcl_Stat (as well as Tcl_OpenFileChannelProc) hook into a linked list of functions. This allows the possibility to reroute file access to alternative media or access methods. Tcl_Access checks whether the process would be allowed to read, write or test for existence of the file (or other file system object) whose name is pathname. If pathname is a symbolic link on Unix, then permissions of the file referred by this symbolic link are tested. On success (all requested permissions granted), zero is returned. On error (at least one bit in mode asked for a permission that is denied, or some other error occurred), -1 is returned. Tcl_Stat fills the stat structure statPtr with information about the specified file. You do not need any access rights to the file to get this information but you need search rights to all directories named in the path leading to the file. The stat structure includes info regarding device, inode (always 0 on Windows), privilege mode, nlink (always 1 on Windows), user id (always 0 on Windows), group id (always 0 on Windows), rdev (same as device on Windows), size, last access time, last modification time, and creation time. If path exists, Tcl_Stat returns 0 and the stat structure is filled with data. Otherwise, -1 is returned, and no stat info is given. KEYWORDS
stat, access Tcl 8.1 Tcl_Access(3)
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