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Work on POSIX-like read() and lseek() support.

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This commit is contained in:
Andreas Kling 2018-10-14 21:19:27 +02:00
parent 9f9b4a2382
commit c94044a04a
Notes: sideshowbarker 2024-07-19 18:48:17 +09:00
11 changed files with 201 additions and 36 deletions
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120
VirtualFileSystem/Ext2FileSystem.cpp
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@ -256,6 +256,82 @@ Vector<unsigned> Ext2FileSystem::blockListForInode(const ext2_inode& e2inode) co
return list;
}
ssize_t Ext2FileSystem::readInodeBytes(InodeIdentifier inode, FileOffset offset, size_t count, byte* buffer) const
{
ASSERT(offset >= 0);
ASSERT(inode.fileSystemID() == id());
auto e2inode = lookupExt2Inode(inode.index());
if (!e2inode) {
printf("[ext2fs] readInodeBytes: metadata lookup for inode %u failed\n", inode.index());
return -EIO;
}
#if 0
// FIXME: We can't fail here while the directory traversal depends on this function. :]
if (isDirectory(e2inode->i_mode))
return -EISDIR;
#endif
if (e2inode->i_size == 0)
return 0;
// Symbolic links shorter than 60 characters are store inline inside the i_block array.
// This avoids wasting an entire block on short links. (Most links are short.)
static const unsigned maxInlineSymlinkLength = 60;
if (isSymbolicLink(e2inode->i_mode) && e2inode->i_size < maxInlineSymlinkLength) {
ssize_t nread = min(e2inode->i_size - offset, static_cast<FileOffset>(count));
memcpy(buffer, e2inode->i_block + offset, nread);
return nread;
}
// FIXME: It's grossly inefficient to fetch the blocklist on every call to readInodeBytes().
// It needs to be cached!
auto list = blockListForInode(*e2inode);
if (list.isEmpty()) {
printf("[ext2fs] readInodeBytes: empty block list for inode %u\n", inode.index());
return -EIO;
}
dword firstBlockLogicalIndex = offset / blockSize();
dword lastBlockLogicalIndex = (offset + count) / blockSize();
if (lastBlockLogicalIndex >= list.size())
lastBlockLogicalIndex = list.size() - 1;
dword offsetIntoFirstBlock = offset % blockSize();
ssize_t nread = 0;
size_t remainingCount = min((FileOffset)count, e2inode->i_size - offset);
byte* out = buffer;
#ifdef EXT2_DEBUG
printf("ok let's do it, read(%llu, %u) -> blocks %u thru %u, oifb: %u\n", offset, count, firstBlockLogicalIndex, lastBlockLogicalIndex, offsetIntoFirstBlock);
#endif
for (dword bi = firstBlockLogicalIndex; bi <= lastBlockLogicalIndex; ++bi) {
auto block = readBlock(list[bi]);
if (!block) {
printf("[ext2fs] readInodeBytes: readBlock(%u) failed (lbi: %u)\n", list[bi], bi);
return -EIO;
}
dword offsetIntoBlock;
if (bi == firstBlockLogicalIndex)
offsetIntoBlock = offsetIntoFirstBlock;
else
offsetIntoBlock = 0;
dword numBytesToCopy = min(blockSize() - offsetIntoBlock, remainingCount);
memcpy(out, block.pointer() + offsetIntoBlock, numBytesToCopy);
remainingCount -= numBytesToCopy;
nread += numBytesToCopy;
out += numBytesToCopy;
}
return nread;
}
ByteBuffer Ext2FileSystem::readInode(InodeIdentifier inode) const
{
ASSERT(inode.fileSystemID() == id());
@ -266,41 +342,25 @@ ByteBuffer Ext2FileSystem::readInode(InodeIdentifier inode) const
return nullptr;
}
if (e2inode->i_size == 0)
return ByteBuffer::createEmpty();
auto contents = ByteBuffer::createUninitialized(e2inode->i_size);
// Symbolic links shorter than 60 characters are store inline inside the i_block array.
// This avoids wasting an entire block on short links. (Most links are short.)
static const unsigned maxInlineSymlinkLength = 60;
if (isSymbolicLink(e2inode->i_mode) && e2inode->i_size < maxInlineSymlinkLength) {
auto inlineSymlink = ByteBuffer::createUninitialized(e2inode->i_size);
memcpy(inlineSymlink.pointer(), e2inode->i_block, e2inode->i_size);
return inlineSymlink;
ssize_t nread;
byte buffer[512];
byte* out = contents.pointer();
FileOffset offset = 0;
for (;;) {
nread = readInodeBytes(inode, offset, sizeof(buffer), buffer);
if (nread <= 0)
break;
memcpy(out, buffer, nread);
out += nread;
offset += nread;
}
auto list = blockListForInode(*e2inode);
if (list.isEmpty()) {
printf("[ext2fs] readInode: empty block list for inode %u\n", inode.index());
if (nread < 0) {
printf("[ext2fs] readInode: ERROR: %d\n", nread);
return nullptr;
}
auto contents = ByteBuffer::createUninitialized(list.size() * blockSize());
auto* out = contents.pointer();
for (unsigned i = 0; i < list.size(); ++i) {
auto block = readBlock(list[i]);
if (!block) {
printf("[ext2fs] readInode: readBlock(%u) failed\n", list[i]);
return nullptr;
}
memcpy(out, block.pointer(), block.size());
out += blockSize();
}
#ifdef EXT2_DEBUG
printf("trim from %u to %u\n", contents.size(), e2inode->i_size);
#endif
contents.trim(e2inode->i_size);
return contents;
}