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Kernel/FileSystem: Fix handling of FAT names that don't fill an entry

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* Fix bug where last character of a filename or extension would be
   truncated (HELLO.TXT -> HELL.TX).
 * Fix bug where additional NULL characters would be added to long
   filenames that did not completely fill one of the Long Filename Entry
   character fields.
This commit is contained in:
Taj Morton 2022-12-31 13:01:26 -08:00 committed by Sam Atkins
parent f2253d11e5
commit 31eeea08ba
Notes: sideshowbarker 2024-07-17 21:16:31 +09:00 
Author: https://github.com/tajmorton
Commit: https://github.com/SerenityOS/serenity/commit/31eeea08ba
Pull-request: https://github.com/SerenityOS/serenity/pull/16754
Reviewed-by: https://github.com/AtkinsSJ ✅
2 changed files with 17 additions and 3 deletions
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17
Kernel/FileSystem/FATFS/Inode.cpp
View File

@ -167,7 +167,20 @@ ErrorOr<NonnullOwnPtr<KString>> FATInode::compute_filename(FATEntry& entry, Vect
filename.append(lfn_entry.characters3[1]);
}
return TRY(KString::try_create(byte_terminated_string(filename.string_view(), lfn_entry_text_termination)));
// Long Filenames have two terminators:
// 1. Completely unused "entries" (the `characterN` fields of
// `lfn_entry`) are filled with 0xFF (`lfn_entry_unused_byte`).
// 2. Partially used entries (within `characterN`) are null-padded.
//
// `filename` is truncated first to eliminate unused entries, and
// then further truncated to remove any existing null padding characters.
//
// Page 8 of the Long Filename Specification
// (http://www.osdever.net/documents/LongFileName.pdf)
// details this encoding ("If the long name does not fill...").
return TRY(KString::try_create(
byte_terminated_string(
byte_terminated_string(filename.string_view(), lfn_entry_unused_byte), lfn_entry_character_termination)));
}
VERIFY_NOT_REACHED();
@ -184,7 +197,7 @@ Time FATInode::fat_date_time(FATPackedDate date, FATPackedTime time)
StringView FATInode::byte_terminated_string(StringView string, u8 fill_byte)
{
if (auto index = string.find_last_not(fill_byte); index.has_value())
return string.substring_view(0, index.value());
return string.substring_view(0, index.value() + 1);
return string;
}

3
Kernel/FileSystem/FATFS/Inode.h
View File

@ -36,7 +36,8 @@ private:
static constexpr u8 end_entry_byte = 0x00;
static constexpr u8 unused_entry_byte = 0xE5;
static constexpr u8 lfn_entry_text_termination = 0xFF;
static constexpr u8 lfn_entry_character_termination = 0x00;
static constexpr u8 lfn_entry_unused_byte = 0xFF;
static constexpr u16 first_fat_year = 1980;