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File system WIP

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Daniel Hillerström
2021-01-14 20:00:46 +00:00
parent 46e36b5318
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2 changed files with 99 additions and 24 deletions
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4
macros.tex
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@@ -362,7 +362,7 @@
\newcommand{\Putc}{\dec{Putc}} \newcommand{\Putc}{\dec{Putc}}
\newcommand{\putc}{\dec{putc}} \newcommand{\putc}{\dec{putc}}
\newcommand{\UFile}{\dec{File}} \newcommand{\UFile}{\dec{File}}
\newcommand{\UFD}{\dec{INumber}} \newcommand{\UFD}{\dec{FileDescr}}
\newcommand{\fwrite}{\dec{fwrite}} \newcommand{\fwrite}{\dec{fwrite}}
\newcommand{\iter}{\dec{iter}} \newcommand{\iter}{\dec{iter}}
\newcommand{\stdout}{\dec{stdout}} \newcommand{\stdout}{\dec{stdout}}
@@ -423,6 +423,8 @@
\newcommand{\lookup}{\dec{lookup}} \newcommand{\lookup}{\dec{lookup}}
\newcommand{\modify}{\dec{modify}} \newcommand{\modify}{\dec{modify}}
\newcommand{\fileIO}{\dec{fileIO}} \newcommand{\fileIO}{\dec{fileIO}}
\newcommand{\ULink}{\dec{Link}}
\newcommand{\UUnlink}{\dec{Unlink}}
%% %%
%% Some control operators %% Some control operators

119
thesis.tex
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@@ -4835,10 +4835,10 @@ operation $\Write$ for writing a list of characters to the file.
\BIO \defas \{\Write : \Record{\UFD;\String} \opto \UnitType\} \BIO \defas \{\Write : \Record{\UFD;\String} \opto \UnitType\}
\] \]
% %
The operation is parameterised by an $\UFD$ and a character The operation is parameterised by a $\UFD$ and a character
sequence. We will leave the $\UFD$ type abstract until sequence. We will leave the $\UFD$ type abstract until
Section~\ref{sec:tiny-unix-io}, however, we will assume the existence Section~\ref{sec:tiny-unix-io}, however, we shall assume the existence
of a term $\stdout : \UFD$ such that we perform invocations of of a term $\stdout : \UFD$ such that we can perform invocations of
$\Write$. $\Write$.
% %
Let us define a suitable handler for this operation. Let us define a suitable handler for this operation.
@@ -4877,10 +4877,15 @@ The $\Write$-case extends the file by first invoking the resumption,
whose return type is the same as the handler's return type, thus it whose return type is the same as the handler's return type, thus it
returns a pair containing the result of $m$ and the file state. The returns a pair containing the result of $m$ and the file state. The
file gets extended with the character sequence $cs$ before it is file gets extended with the character sequence $cs$ before it is
returned along with the original result of $m$.% The file is returned along with the original result of $m$.
% effectively built bottom up starting with the last character. %
Intuitively, we may think of this implementation of $\Write$ as a
peculiar instance of buffered writing, where the contents of the
operation are committed to the file in last-in-first-out order,
i.e. the contents of the last write will be committed first.
Let us define an auxiliary function that writes a string to the $\stdout$ file. Let us define an auxiliary function that writes a string to the
$\stdout$ file.
% %
\[ \[
\bl \bl
@@ -5275,8 +5280,8 @@ $\False$. The results are joined by list concatenation ($\concat$).
% %
Thus the handler returns a list of all the possible results of $m$. Thus the handler returns a list of all the possible results of $m$.
% %
In fact, this handler is exactly the handler for nondeterministic In fact, this handler is exactly the standard handler for
choice, and it satisfies the standard semi-lattice nondeterministic choice, which satisfies the standard semi-lattice
equations~\cite{PlotkinP09,PlotkinP13}. equations~\cite{PlotkinP09,PlotkinP13}.
% \dhil{This is an instance of non-blind backtracking~\cite{FriedmanHK84}} % \dhil{This is an instance of non-blind backtracking~\cite{FriedmanHK84}}
@@ -5752,7 +5757,7 @@ evaluation of the stateful fragment of $m$ to continue.
\dhil{Discuss briefly local vs global state~\cite{PauwelsSM19}} \dhil{Discuss briefly local vs global state~\cite{PauwelsSM19}}
\subsubsection{Basic sequential file system} \subsubsection{Basic serial file system}
% %
\begin{figure}[t] \begin{figure}[t]
\centering \centering
@@ -5827,7 +5832,7 @@ files~\cite{RitchieT74}. An ordinary file is a sequence of
characters. A directory file is a container for all kinds of files. A characters. A directory file is a container for all kinds of files. A
special file is an interface for interacting with an i/o device. special file is an interface for interacting with an i/o device.
We will implement a \emph{basic sequential file system}, which we dub We will implement a \emph{basic serial file system}, which we dub
\fsname{}. \fsname{}.
% %
It will be basic in the sense that it models the bare minimum to pass It will be basic in the sense that it models the bare minimum to pass
@@ -5835,9 +5840,9 @@ as a file system, that is we will implement support for the four basic
operations: file allocation, file deletion, file reading, and file operations: file allocation, file deletion, file reading, and file
writing. writing.
% %
The system will support sequential read and write operations. This The read and write operations will be serial, meaning every file is
means every file is read in order from its first character to its read in order from its first character to its last character, and
character, and every file is written to by appending the new content. every file is written to by appending the new content.
% %
\fsname{} will only contain ordinary files, and as a result \fsname{} will only contain ordinary files, and as a result
the file hierarchy will be entirely flat. Although, the system can the file hierarchy will be entirely flat. Although, the system can
@@ -5846,8 +5851,11 @@ extra complexity, that blurs rather than illuminates the model.
\paragraph{Directory, i-list, and data region} \paragraph{Directory, i-list, and data region}
% %
The core of \fsname{} comprises three structures to manage interaction A storage medium is an array of bytes. An \UNIX{} file system is
with files. implemented on top of this array by interpreting certain intervals of
the array differently. These intervals provide the space for the
essential administrative structures for file organisation.
%
\begin{enumerate} \begin{enumerate}
\item The \emph{directory} is a collection of human-readable names for \item The \emph{directory} is a collection of human-readable names for
files. In general, a file may have multiple names. Each name is files. In general, a file may have multiple names. Each name is
@@ -5858,13 +5866,13 @@ with files.
\item The \emph{data region} contains the actual file contents. \item The \emph{data region} contains the actual file contents.
\end{enumerate} \end{enumerate}
% %
\dhil{Motivate i-nodes, etc. Real UNIX file system use those structures. Admit simplification: no file handles; no resource leakage} These structures make up the \fsname{}.
% %
Figure~\ref{fig:unix-mappings} depicts an example with the three Figure~\ref{fig:unix-mappings} depicts an example with the three
structures and a mapping between them. structures and a mapping between them.
% %
The only file meta-data tracked by \fsname{} is the number of names The only file metadata tracked by \fsname{} is the number of names for
for a file. a file.
% %
The three structures and their mappings can be implemented using The three structures and their mappings can be implemented using
association lists. Although, a better practical choice may be a association lists. Although, a better practical choice may be a
@@ -5921,6 +5929,16 @@ Initially the file system contains a single, empty file with the name
$\texttt{stdout}$. Next we will implement the basic operations on the $\texttt{stdout}$. Next we will implement the basic operations on the
file system separately. file system separately.
We have made a gross simplification here, as a typical file system
would provide some \emph{file descriptor} abstraction for managing
access open files. In \fsname{} we will operate directly on i-nodes,
meaning we define $\UFD \defas \Int$, meaning the file open operation
will return an i-node identifier. As consequence it does not matter
whether a file is closed after use as file closing would be a no-op
(closing a file does not change the state of its i-node). Therefore
\fsname{} will not provide a close operation. As a further consequence
the file system will have no resource leakage.
\paragraph{File reading and writing} \paragraph{File reading and writing}
% %
Let us begin by giving a semantics to file reading and writing. We Let us begin by giving a semantics to file reading and writing. We
@@ -6065,12 +6083,38 @@ $\fwrite$. Failure is interpreted as unit, meaning that from the
caller perspective the operation fails silently. caller perspective the operation fails silently.
\paragraph{File creation and opening} \paragraph{File creation and opening}
The signature of file creation and opening is unsurprisingly comprised
of two operations.
% %
\dhil{TODO}
\[ \[
\dec{FileCO} \defas \{\UCreate : \String \opto \Int; \UOpen : \String \opto \Option~\Int\} \dec{FileCO} \defas \{\UCreate : \String \opto \Int; \UOpen : \String \opto \Option~\Int\}
\] \]
% %
The implementation of file creation and opening follows the same
pattern as the implementation of reading and writing. As before, we
implement a primitive routine for each operation that interacts
directly with the file system structure. We start with the
implementation of primitive file opening function as file creation
function depends on this function.
%
\[
\bl
\fopen : \Record{\String;\FileSystem} \to \Int \eff \{\Fail : \UnitType \opto \Zero\}\\
\fopen\,\Record{fname;fs} \defas \lookup\,\Record{fname; fs.dir}
\el
\]
\[
\bl
\fcreate : \Record{\String;\FileSystem} \to \Record{\Int;\FileSystem} \eff \{\Fail : \UnitType \opto \Zero\}\\
\fcreate\,\Record{fname;fs} \defas
\ba[t]{@{}l}
\Let\;inode \revto \lookup\,\Record{ino; fs.ilist}\;\In\\
\lookup\,\Record{inode.loc; fs.dreg}
\el
\el
\]
%
\[ \[
\bl \bl
\fileAlloc : (\UnitType \to \alpha \eff \dec{FileCO}) \to \alpha \eff \State~\FileSystem\\ \fileAlloc : (\UnitType \to \alpha \eff \dec{FileCO}) \to \alpha \eff \State~\FileSystem\\
@@ -6101,15 +6145,12 @@ caller perspective the operation fails silently.
% %
There is no file close operation in \fsname{}, because it would be a no-op. There is no file close operation in \fsname{}, because it would be a no-op.
\paragraph{File linking and unlinking}
\dhil{Maybe axe\dots} \medskip\\
The composition of $\fileRW$ and $\fileAlloc$ give a semantics to file The composition of $\fileRW$ and $\fileAlloc$ give a semantics to file
i/o. i/o.
% %
\[ \[
\bl \bl
\fileIO : (\UnitType \to \alpha \eff \{\dec{FileCO},\dec{FileRW}\}) \to \alpha \eff \State~\FileSystem \\ \fileIO : (\UnitType \to \alpha \eff \{\dec{FileCO};\dec{FileRW}\}) \to \alpha \eff \State~\FileSystem \\
\fileIO~m \defas \dec{fileCO}\,(\lambda\Unit. \dec{fileRW}\,m) \fileIO~m \defas \dec{fileCO}\,(\lambda\Unit. \dec{fileRW}\,m)
\el \el
\] \]
@@ -6224,6 +6265,38 @@ We can now plug everything together.
\el \el
\ea \ea
\] \]
%
\subsubsection{File linking and unlinking}
\[
\bl
\dec{cp} : \Record{\Bool;\String;\String} \to \UnitType \eff \{\ULink : \Record{\String;\String} \opto \UnitType;\dec{FileCO};\dec{FileRW}\}\\
\dec{cp}~\Record{link;src;dest} \defas
\bl
\If\;link\;\Then\;\Do\;\ULink\,\Record{src;dest}\\
\Else\; \bl
\Case\;\Do\;\UOpen~src\\
\{ \ba[t]{@{~}l@{~}c@{~}l}
\None &\mapsto& \Unit\\
\Some~ino &\mapsto& \\
\multicolumn{3}{l}{\quad\Case\;\Do\;\URead~ino\;\{
\ba[t]{@{~}l@{~}c@{~}l}
\None &\mapsto& \Unit\\
\Some~cs &\mapsto& \echo~cs~\redirect~dest \} \}
\ea}
\ea
\el
\el
\el
\]
\[
\bl
\dec{rm} : \String \to \UnitType \eff \{\UUnlink : \String \opto \UnitType\}\\
\dec{rm}~fname \defas \Do\;\UUnlink~fname
\el
\]
% \begin{figure}[t] % \begin{figure}[t]
% \centering % \centering
% \begin{tikzpicture}[node distance=4cm,auto,>=stealth'] % \begin{tikzpicture}[node distance=4cm,auto,>=stealth']