path: root/tasks/16/readme
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authorBryan Brattlof <hello@bryanbrattlof.com>2020-07-15 16:37:01 -0400
committerBryan Brattlof <hello@bryanbrattlof.com>2020-07-15 16:37:01 -0400
commit96e2a9dbe1851c8cbb4e80511fa1d77401149101 (patch)
tree03c7663dc17a8f6ae96d3209b413672d0cbb4660 /tasks/16/readme
parent4f27198d12f7efb3514277c8ac3d3cf1ceb7a56d (diff)
task 16: add task readme
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+Task 16
+Good job with the new syscall. The odds of you ever having to write a
+new syscall is pretty rare, but now you know where to look them up, and
+what the code involved in creating one looks like, which is useful when
+you try to debug things.
+Let's take a breather after all of that code, and go back to doing a bit
+of reading, and learn some more about some common kernel tools.
+Go install the tool 'sparse'. It was started by Linus as a
+static-analysis tool that acts much like a compiler. The kernel build
+system is set up to have it run if you ask it to, and it will report a
+bunch of issues in C code that are really specific to the kernel.
+When you build the kernel, pass the "C=1" option to the build, to have
+sparse run on the .c file before gcc is run. Depending on the file,
+nothing might be printed out, or something might. Here's an example of
+it being run on the ext4 code:
+$ make C=1 M=fs/ext4
+ CHECK fs/ext4/balloc.c
+ CC fs/ext4/balloc.o
+ CHECK fs/ext4/bitmap.c
+ CC fs/ext4/bitmap.o
+ CHECK fs/ext4/dir.c
+ CC fs/ext4/dir.o
+ CHECK fs/ext4/file.c
+ CC fs/ext4/file.o
+ CHECK fs/ext4/fsync.c
+ CC fs/ext4/fsync.o
+ CHECK fs/ext4/ialloc.c
+ CC fs/ext4/ialloc.o
+ CHECK fs/ext4/inode.c
+ CC fs/ext4/inode.o
+ CHECK fs/ext4/page-io.c
+ CC fs/ext4/page-io.o
+ CHECK fs/ext4/ioctl.c
+ CC fs/ext4/ioctl.o
+ CHECK fs/ext4/namei.c
+ CC fs/ext4/namei.o
+ CHECK fs/ext4/super.c
+ CC fs/ext4/super.o
+ CHECK fs/ext4/symlink.c
+ CC fs/ext4/symlink.o
+ CHECK fs/ext4/hash.c
+ CC fs/ext4/hash.o
+ CHECK fs/ext4/resize.c
+ CC fs/ext4/resize.o
+ CHECK fs/ext4/extents.c
+ CC fs/ext4/extents.o
+ CHECK fs/ext4/ext4_jbd2.c
+ CC fs/ext4/ext4_jbd2.o
+ CHECK fs/ext4/migrate.c
+ CC fs/ext4/migrate.o
+ CHECK fs/ext4/mballoc.c
+fs/ext4/mballoc.c:5018:9: warning: context imbalance in 'ext4_trim_extent' - unexpected unlock
+ CC fs/ext4/mballoc.o
+ CHECK fs/ext4/block_validity.c
+ CC fs/ext4/block_validity.o
+ CHECK fs/ext4/move_extent.c
+ CC fs/ext4/move_extent.o
+ CHECK fs/ext4/mmp.c
+ CC fs/ext4/mmp.o
+ CHECK fs/ext4/indirect.c
+ CC fs/ext4/indirect.o
+ CHECK fs/ext4/extents_status.c
+ CC fs/ext4/extents_status.o
+ CHECK fs/ext4/xattr.c
+ CC fs/ext4/xattr.o
+ CHECK fs/ext4/xattr_user.c
+ CC fs/ext4/xattr_user.o
+ CHECK fs/ext4/xattr_trusted.c
+ CC fs/ext4/xattr_trusted.o
+ CHECK fs/ext4/inline.c
+ CC fs/ext4/inline.o
+ CHECK fs/ext4/acl.c
+ CC fs/ext4/acl.o
+ CHECK fs/ext4/xattr_security.c
+ CC fs/ext4/xattr_security.o
+ LD fs/ext4/ext4.o
+ LD fs/ext4/built-in.o
+ Building modules, stage 2.
+ MODPOST 0 modules
+As you can see, only one warning was found here, and odds are, it is a
+false-positive, as I'm sure those ext4 developers know what they are
+doing with their locking functions, right?
+Anyway the task this time is:
+ - Run sparse on the drivers/staging/ directory, yes, that horrible
+ code again, sorry.
+ - Find one warning that looks interesting.
+ - Write a patch that resolves the issue.
+ - Make sure the patch is correct by running it through
+ scripts/checkpatch.pl
+ - Submit the code to the maintainer of the driver/subsystem, finding
+ the proper name and mailing lists to send it to by running the tool,
+ scripts/get_maintainer.pl on your patch.
+ - Send a web link back to me of your patch in the public mailing list
+ archive (don't cc: me on the patch, that will only confuse me and
+ everyone in the kernel development community.)
+ - If you want to mention the Eudyptula Challenge as the reason for
+ writing the patch, feel free to do so in the body of the patch, but
+ it's not necessary at all.
+That's it, much like task 10 was, but this time you are fixing logical
+issues, not just pesky coding style issues. You are a real developer
+now, fixing real bugs!