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Kernel: Remove allocations from path lookup

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this bumped looped /usr/bin/ls stat performance from 750k->1100k/s
This commit is contained in:
Bananymous
2026-05-26 17:48:56 +03:00
parent 16a442f473
commit 98fd86477a
1 changed files with 55 additions and 52 deletions
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107
kernel/kernel/FS/VirtualFileSystem.cpp
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@@ -233,44 +233,45 @@ namespace Kernel
return nullptr; return nullptr;
} }
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstack-usage="
BAN::ErrorOr<VirtualFileSystem::File> VirtualFileSystem::file_from_relative_path(BAN::RefPtr<Inode> root_inode, const File& parent, const Credentials& credentials, BAN::StringView path, int flags) BAN::ErrorOr<VirtualFileSystem::File> VirtualFileSystem::file_from_relative_path(BAN::RefPtr<Inode> root_inode, const File& parent, const Credentials& credentials, BAN::StringView path, int flags)
{ {
auto inode = parent.inode; auto inode = parent.inode;
ASSERT(inode); ASSERT(inode);
BAN::String canonical_path; char canonical_buf[PATH_MAX];
TRY(canonical_path.append(parent.canonical_path)); size_t canonical_len = parent.canonical_path.size();
if (!canonical_path.empty() && canonical_path.back() == '/') if (!parent.canonical_path.empty() && parent.canonical_path.back() == '/')
canonical_path.pop_back(); canonical_len--;
ASSERT(canonical_path.empty() || canonical_path.back() != '/'); memcpy(canonical_buf, parent.canonical_path.data(), canonical_len);
ASSERT(canonical_len == 0 || canonical_buf[canonical_len - 1] != '/');
BAN::Vector<BAN::String> path_parts; char path_storage[PATH_MAX];
const auto append_string_view_in_reverse =
[&path_parts](BAN::StringView path) -> BAN::ErrorOr<void>
{
auto split_path = TRY(path.split('/'));
TRY(path_parts.reserve(path_parts.size() + split_path.size()));
for (size_t i = split_path.size(); i > 0; i--)
{
TRY(path_parts.emplace_back());
TRY(path_parts.back().append(split_path[i - 1]));
}
return {};
};
TRY(append_string_view_in_reverse(path));
size_t link_depth = 0; size_t link_depth = 0;
for (;;)
while (!path_parts.empty())
{ {
BAN::String path_part = BAN::move(path_parts.back()); const auto path_part = [&path] {
path_parts.pop_back(); size_t off = 0;
while (off < path.size() && path[off] == '/')
off++;
if (path_part.empty() || path_part == "."_sv) size_t len = 0;
while (off + len < path.size() && path[off + len] != '/')
len++;
const auto result = path.substring(off, len);
path = path.substring(off + len);
return result;
}();
if (path_part.empty())
break;
if (path_part == "."_sv)
continue; continue;
auto orig = inode; auto orig_inode = inode;
// resolve file name // resolve file name
{ {
@@ -287,26 +288,26 @@ namespace Kernel
if (path_part == ".."_sv) if (path_part == ".."_sv)
{ {
if (!canonical_path.empty()) while (canonical_len && canonical_buf[canonical_len - 1] != '/')
{ canonical_len--;
ASSERT(canonical_path.front() == '/'); if (canonical_len)
while (canonical_path.back() != '/') canonical_len--;
canonical_path.pop_back();
canonical_path.pop_back();
}
} }
else else
{ {
if (auto* mount_point = mount_from_host_inode(inode)) if (auto* mount_point = mount_from_host_inode(inode))
inode = mount_point->target->root_inode(); inode = mount_point->target->root_inode();
TRY(canonical_path.push_back('/')); if (canonical_len + 1 + path_part.size() > sizeof(canonical_buf))
TRY(canonical_path.append(path_part)); return BAN::Error::from_errno(ENAMETOOLONG);
canonical_buf[canonical_len++] = '/';
memcpy(canonical_buf + canonical_len, path_part.data(), path_part.size());
canonical_len += path_part.size();
} }
} }
if (!inode->mode().iflnk()) if (!inode->mode().iflnk())
continue; continue;
if ((flags & O_NOFOLLOW) && path_parts.empty()) if ((flags & O_NOFOLLOW) && !path.find([](char ch) { return ch != '/'; }).has_value())
continue; continue;
// resolve symbolic links // resolve symbolic links
@@ -318,21 +319,26 @@ namespace Kernel
if (link_target.front() == '/') if (link_target.front() == '/')
{ {
inode = root_inode; inode = root_inode;
canonical_path.clear(); canonical_len = 0;
} }
else else
{ {
inode = orig; inode = orig_inode;
while (canonical_path.back() != '/') while (canonical_len && canonical_buf[canonical_len - 1] != '/')
canonical_path.pop_back(); canonical_len--;
canonical_path.pop_back(); if (canonical_len)
canonical_len--;
} }
TRY(append_string_view_in_reverse(link_target.sv())); if (link_target.size() + path.size() > sizeof(path_storage))
return BAN::Error::from_errno(ENAMETOOLONG);
memcpy(path_storage, link_target.data(), link_target.size());
memcpy(path_storage + link_target.size(), path.data(), path.size());
path = BAN::StringView(path_storage, link_target.size() + path.size());
link_depth++; link_depth++;
if (link_depth > 100) if (link_depth > SYMLOOP_MAX)
return BAN::Error::from_errno(ELOOP); return BAN::Error::from_errno(ELOOP);
} }
} }
@@ -340,17 +346,14 @@ namespace Kernel
if (!inode->can_access(credentials, flags)) if (!inode->can_access(credentials, flags))
return BAN::Error::from_errno(EACCES); return BAN::Error::from_errno(EACCES);
if (canonical_path.empty()) if (canonical_len == 0)
TRY(canonical_path.push_back('/')); canonical_buf[canonical_len++] = '/';
File file; BAN::String canonical_path;
file.inode = inode; TRY(canonical_path.append(BAN::StringView(canonical_buf, canonical_len)));
file.canonical_path = BAN::move(canonical_path);
if (file.canonical_path.empty()) return File(BAN::move(inode), BAN::move(canonical_path));
TRY(file.canonical_path.push_back('/'));
return file;
} }
#pragma GCC diagnostic pop
} }