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/*************************************************************************** |
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* Copyright (c) 2024 Microsoft Corporation |
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* Copyright (c) 2026-present Eclipse ThreadX contributors |
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* |
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* This program and the accompanying materials are made available under the |
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* terms of the MIT License which is available at |
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* https://opensource.org/licenses/MIT. |
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* |
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* SPDX-License-Identifier: MIT |
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**************************************************************************/ |
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/**************************************************************************/ |
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/**************************************************************************/ |
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/** */ |
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/** FileX Component */ |
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/** */ |
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/** File */ |
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/** */ |
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/**************************************************************************/ |
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/**************************************************************************/ |
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#define FX_SOURCE_CODE |
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/* Include necessary system files. */ |
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#include "fx_api.h" |
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#include "fx_system.h" |
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#include "fx_directory.h" |
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#include "fx_file.h" |
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#include "fx_utility.h" |
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/**************************************************************************/ |
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/* */ |
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/* FUNCTION RELEASE */ |
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/* */ |
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/* _fx_file_extended_seek PORTABLE C */ |
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/* 6.1.7 */ |
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/* AUTHOR */ |
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/* */ |
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/* William E. Lamie, Microsoft Corporation */ |
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/* */ |
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/* DESCRIPTION */ |
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/* */ |
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/* This function positions the internal file pointers to the specified */ |
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/* byte offset such that the next read or write operation will be */ |
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/* performed there. If the byte offset is greater than the size, the */ |
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/* file pointers will be positioned to the end of the file. */ |
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/* */ |
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/* INPUT */ |
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/* */ |
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/* file_ptr File control block pointer */ |
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/* byte_offset Byte offset into the file */ |
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/* */ |
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/* OUTPUT */ |
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/* */ |
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/* return status */ |
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/* */ |
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/* CALLS */ |
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/* */ |
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/* _fx_utility_FAT_entry_read Read a FAT entry */ |
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/* */ |
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/* CALLED BY */ |
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/* */ |
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/* Application Code */ |
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/* */ |
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/**************************************************************************/ |
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UINT _fx_file_extended_seek(FX_FILE *file_ptr, ULONG64 byte_offset) |
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{ |
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UINT status; |
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ULONG cluster; |
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ULONG contents = 0; |
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ULONG bytes_per_cluster; |
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ULONG last_cluster; |
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ULONG cluster_count; |
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ULONG64 bytes_remaining; |
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FX_MEDIA *media_ptr; |
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/* First, determine if the file is still open. */ |
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✓✓ |
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if (file_ptr -> fx_file_id != FX_FILE_ID) |
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{ |
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/* Return the file not open error status. */ |
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return(FX_NOT_OPEN); |
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} |
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#ifndef FX_MEDIA_STATISTICS_DISABLE |
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/* Setup pointer to media structure. */ |
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media_ptr = file_ptr -> fx_file_media_ptr; |
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/* Increment the number of times this service has been called. */ |
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media_ptr -> fx_media_file_seeks++; |
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#endif |
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/* Setup pointer to associated media control block. */ |
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media_ptr = file_ptr -> fx_file_media_ptr; |
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/* If trace is enabled, insert this event into the trace buffer. */ |
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FX_TRACE_IN_LINE_INSERT(FX_TRACE_FILE_SEEK, file_ptr, byte_offset, file_ptr -> fx_file_current_file_offset, 0, FX_TRACE_FILE_EVENTS, 0, 0) |
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/* Protect against other threads accessing the media. */ |
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FX_PROTECT |
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/* Check if we actually have to do anything. */ |
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✓✓ |
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if (byte_offset == file_ptr -> fx_file_current_file_offset) |
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{ |
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/* Release media protection. */ |
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FX_UNPROTECT |
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/* Seek is complete, return successful status. */ |
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return(FX_SUCCESS); |
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} |
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/* Calculate the number of bytes per cluster. */ |
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bytes_per_cluster = ((ULONG)media_ptr -> fx_media_bytes_per_sector) * |
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((ULONG)media_ptr -> fx_media_sectors_per_cluster); |
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/* Check for invalid value. */ |
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✓✓ |
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if (bytes_per_cluster == 0) |
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{ |
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/* Release media protection. */ |
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FX_UNPROTECT |
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/* Invalid media, return error. */ |
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return(FX_MEDIA_INVALID); |
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} |
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/* See if we need to adjust the byte offset. */ |
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✓✓ |
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if (byte_offset > file_ptr -> fx_file_current_file_size) |
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{ |
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/* Adjust the byte offset down to the file size. */ |
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byte_offset = file_ptr -> fx_file_current_file_size; |
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} |
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/* Check if the desired position within the leading consecutive clusters. */ |
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✓✓ |
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if (byte_offset >= (ULONG64)file_ptr -> fx_file_consecutive_cluster * (ULONG64)bytes_per_cluster) |
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{ |
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/* At this point, we are ready to walk list of clusters to setup the |
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seek position of this file. */ |
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/* check if byte_offset is greater than where we were left off earlier */ |
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✓✓ |
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if ((ULONG64)file_ptr -> fx_file_current_relative_cluster * (ULONG64)bytes_per_cluster < byte_offset) |
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{ |
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cluster = file_ptr -> fx_file_current_physical_cluster; |
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bytes_remaining = byte_offset - |
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file_ptr -> fx_file_current_relative_cluster * bytes_per_cluster; |
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cluster_count = file_ptr -> fx_file_current_relative_cluster; |
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} |
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else |
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{ |
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cluster = file_ptr -> fx_file_first_physical_cluster + |
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(file_ptr -> fx_file_consecutive_cluster - 1); |
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bytes_remaining = byte_offset - |
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(file_ptr -> fx_file_consecutive_cluster - 1) * bytes_per_cluster; |
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cluster_count = (file_ptr -> fx_file_consecutive_cluster - 1); |
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} |
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/* Follow the link of FAT entries. */ |
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✓✓✓✓
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while ((cluster >= FX_FAT_ENTRY_START) && (cluster < media_ptr -> fx_media_fat_reserved)) |
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{ |
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/* Increment the number of clusters. */ |
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cluster_count++; |
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/* Read the current cluster entry from the FAT. */ |
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status = _fx_utility_FAT_entry_read(media_ptr, cluster, &contents); |
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/* Check the return value. */ |
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✓✓ |
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if (status != FX_SUCCESS) |
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{ |
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/* Release media protection. */ |
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FX_UNPROTECT |
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/* Return the error status. */ |
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return(status); |
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} |
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/* Save the last valid cluster. */ |
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last_cluster = cluster; |
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/* Setup for the next cluster. */ |
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cluster = contents; |
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/* Determine if this is the last written cluster. */ |
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✓✓ |
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if (bytes_remaining > bytes_per_cluster) |
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{ |
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/* Still more seeking, just decrement the working byte offset. */ |
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bytes_remaining = bytes_remaining - bytes_per_cluster; |
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} |
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else |
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{ |
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/* Remember this cluster number. */ |
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file_ptr -> fx_file_current_physical_cluster = last_cluster; |
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/* Remember the relative cluster. */ |
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file_ptr -> fx_file_current_relative_cluster = cluster_count - 1; |
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/* If the remaining bytes exactly fits the cluster size, check for |
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a possible adjustment to the next cluster. */ |
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✓✓✓✓
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if ((bytes_remaining == bytes_per_cluster) && |
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✓✓ |
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(cluster >= FX_FAT_ENTRY_START) && (cluster < media_ptr -> fx_media_fat_reserved)) |
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{ |
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/* We need to position to next allocated cluster. */ |
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file_ptr -> fx_file_current_physical_cluster = cluster; |
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file_ptr -> fx_file_current_relative_cluster++; |
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/* Clear the remaining bytes. */ |
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bytes_remaining = 0; |
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} |
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/* This is the cluster that contains the seek position. */ |
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break; |
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} |
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} |
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/* Check for errors in traversal of the FAT chain. */ |
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✓✓ |
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if (byte_offset > (((ULONG64) bytes_per_cluster) * ((ULONG64) cluster_count))) |
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{ |
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/* Release media protection. */ |
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FX_UNPROTECT |
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/* This is an error that suggests a corrupt file. */ |
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return(FX_FILE_CORRUPT); |
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} |
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} |
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else |
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{ |
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/* we should directly access the desired cluster */ |
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file_ptr -> fx_file_current_relative_cluster = (ULONG)(byte_offset / bytes_per_cluster); |
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file_ptr -> fx_file_current_physical_cluster = |
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file_ptr -> fx_file_first_physical_cluster + file_ptr -> fx_file_current_relative_cluster; |
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bytes_remaining = byte_offset % bytes_per_cluster; |
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} |
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/* Determine if the remaining bytes fit exactly into the cluster size. */ |
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✓✓ |
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if (bytes_remaining == bytes_per_cluster) |
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{ |
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/* Position to the end of the cluster. */ |
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file_ptr -> fx_file_current_logical_sector = (ULONG)(((ULONG)media_ptr -> fx_media_data_sector_start) + |
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(((ULONG64)file_ptr -> fx_file_current_physical_cluster - FX_FAT_ENTRY_START) * |
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((ULONG)media_ptr -> fx_media_sectors_per_cluster)) + |
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((bytes_remaining - 1) / (ULONG)media_ptr -> fx_media_bytes_per_sector)); |
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file_ptr -> fx_file_current_relative_sector = (UINT)(((bytes_remaining - 1) / (ULONG)media_ptr -> fx_media_bytes_per_sector)); |
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file_ptr -> fx_file_current_file_offset = byte_offset; |
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file_ptr -> fx_file_current_logical_offset = media_ptr -> fx_media_bytes_per_sector; |
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} |
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else |
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{ |
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/* Position the pointers to the new offset. */ |
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file_ptr -> fx_file_current_logical_sector = (ULONG)(((ULONG)media_ptr -> fx_media_data_sector_start) + |
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(((ULONG64)file_ptr -> fx_file_current_physical_cluster - FX_FAT_ENTRY_START) * |
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((ULONG)media_ptr -> fx_media_sectors_per_cluster)) + |
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(bytes_remaining / (ULONG)media_ptr -> fx_media_bytes_per_sector)); |
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file_ptr -> fx_file_current_relative_sector = (UINT)((bytes_remaining / (ULONG)media_ptr -> fx_media_bytes_per_sector)); |
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file_ptr -> fx_file_current_file_offset = byte_offset; |
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file_ptr -> fx_file_current_logical_offset = (ULONG)(bytes_remaining % ((ULONG)media_ptr -> fx_media_bytes_per_sector)); |
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} |
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/* Release media protection. */ |
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FX_UNPROTECT |
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/* Seek is complete, return successful status. */ |
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return(FX_SUCCESS); |
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} |
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