-@node Project 4--File Systems, Multilevel Feedback Scheduling, Project 3--Virtual Memory, Top
+@node Project 4--File Systems, References, Project 3--Virtual Memory, Top
@chapter Project 4: File Systems
In the previous two assignments, you made extensive use of a
large as the disk. You can assume that the disk will not be larger
than 8 MB. In the basic file system, each file is limited to a file
size of just under 64 kB. Each file has a header called an index node
-or @dfn{inode} (represented by @code{struct inode}) that is a table of
+or @dfn{inode} (represented by @struct{inode}) that is a table of
direct pointers to the disk blocks for that file. Since the inode is
stored in one disk sector, the maximum size of a file is limited by
the number of pointers that will fit in one disk sector. Increasing
Note that write-behind makes your filesystem more fragile in the face
of crashes. Therefore, you should implement some manner to
periodically write all cached blocks to disk. If you have
-@code{timer_sleep()} from the first project working, this is an
+@func{timer_sleep} from the first project working, this is an
excellent application for it.
Likewise, read-ahead is only really useful when done asynchronously.
@item
@b{Will you test our file system with a different @code{DISK_SECTOR_SIZE}?}
-No, @code{DISK_SECTOR_SIZE} will not change.
+No, @code{DISK_SECTOR_SIZE} is fixed at 512. This is a fixed property
+of IDE disk hardware.
@item
-@b{Will the @code{struct inode} take up space on the disk too?}
+@b{Will the @struct{inode} take up space on the disk too?}
-Yes. Anything stored in @code{struct inode} takes up space on disk,
+Yes. Anything stored in @struct{inode} takes up space on disk,
so you must include this in your calculation of how many entires will
fit in a single disk sector.
@end enumerate
The disk we create will be 8 MB or smaller. However, individual files
will have to be smaller than the disk to accommodate the metadata.
-You'll need to consider this when deciding your @code{struct inode}
+You'll need to consider this when deciding your @struct{inode}
organization.
@end enumerate
Yes. Implementing @file{.} and @file{..} is extra credit, though.
@item
-@b{Should @code{remove()} also be able to remove directories?}
+@b{Should @func{remove} also be able to remove directories?}
Yes. The @code{remove} system call should handle removal of both
regular files and directories. You may assume that directories can
@enumerate 1
@item
@b{We're limited to a 64-block cache, but can we also keep a copy of
-each @code{struct inode} for an open file inside @code{struct file},
+each @struct{inode} for an open file inside @struct{file},
the way the stub code does?}
No, you shouldn't keep any disk sectors stored anywhere outside the
cache. That means you'll have to change the way the file
implementation accesses its corresponding inode right now, since it
-currently just creates a new @code{struct inode} in its constructor
+currently just creates a new @struct{inode} in its constructor
and reads the corresponding sector in from disk when it's created.
-There are two reasons for not storing inodes in @code{struct file}.
+There are two reasons for not storing inodes in @struct{file}.
First, keeping extra copies of inodes would be cheating the 64-block
limitation that we place on your cache. Second, if two processes have
the same file open, you will create a huge synchronization headache
-for yourself if each @code{struct file} has its own copy of the inode.
+for yourself if each @struct{file} has its own copy of the inode.
-Note that you can store pointers to inodes in @code{struct file} if
+Note that you can store pointers to inodes in @struct{file} if
you want, and you can store some other small amount of information to
help you find the inode when you need it.
amount of metadata for each of your 64 cache entries, that's fine.
@item
-@b{But why can't we store copies of inodes in @code{struct file}? We
+@b{But why can't we store copies of inodes in @struct{file}? We
don't understand the answer to the previous question.}
-The issue regarding storing @code{struct inode}s has to do with
+The issue regarding storing @struct{inode}s has to do with
implementation of the buffer cache. Basically, you can't store a
-@code{struct inode *} in @code{struct inode}. Each time you need
-to read a @code{struct inode}, you'll have to get it either from the
+@code{struct inode *} in @struct{inode}. Each time you need
+to read a @struct{inode}, you'll have to get it either from the
buffer cache or from disk.
-If you look at @code{file_read_at()}, it uses the inode directly
+If you look at @func{file_read_at}, it uses the inode directly
without having first read in that sector from wherever it was in the
storage hierarchy. You are no longer allowed to do this. You will
need to change @code{file_read_at} (and similar functions) so that it
projects / pintos-anon / blobdiff