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Top Forums Programming write() issue during a low level hdd access Post 302397639 by sponnusa on Monday 22nd of February 2010 09:36:25 PM
Old 02-22-2010
thanks. Will try the linux kernel mailing lists.

Regarding the device interfacing, my requirement deals with a set of data transfers, either be in DMA or PIO mode (for older hdds), in the current program (The one which I've written in assembly in DOS), I move the data to a location, fill up necessary details in the ATA Command Packet, send the command to the HDD ( In DMA Mode), the dma controller and HDD will do the rest.

You are right about the ATAPI timeouts and about the way the calls return to the program. I will be waiting at status registers of the drive to check if the call has passed / failed and proceed further. It sometimes can take more time, in order of milliseconds based on the amount of data I am pointing too at the DMA / PIO buffer in the ATA command packet. And I will not be waiting for the timeout there. (The timeout actually would be the HDD's internal read / write call based) and the result is sent as a signal in one of the status registers as a return value for my actual data transfer call.

I referred to that in my query as the read / write timeout. (I guess I am being a little void in stating my requirements and missing out a lot of key requirements / explanations! Smilie).

It was a good start for me to get into discussion on this board with you and others as to refresh lots of things. It really helps to discuss with a geek (i hope i can address you as one!? Smilie) to get things right and straight at times. (well most of the times!). It was a huge relief after burning mid night oil for weeks at various issues (the current issue was/is still one of the major ones). I think I'll soon be active on this board whenever I can (once I complete my current task and get back home!), helping people.

Switching to the latest kernel has any value addition? Say, any version in 2.6.3?? There were some changes related to RAW or O_DIRECT (I could not remember the exactly) with the newer version.
 

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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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