Changes between Version 4 and Version 5 of FilesystemAPITutorial

Timestamp:

2017-04-09T08:14:42Z (8 years ago)

Author:

Jakub Jermář

Comment:

Add paragraph on unlinking

FilesystemAPITutorial

@@ -91 +91 @@
 == Creating a new directory with a file ==
 
-Imagine we now want to create a new directory `/foo/foobar`, create a file named `hello.txt` and write "Hello world!" to it. Let's start with creating the directory:
+Imagine we now want to create a new directory `/foo/foobar`, then create a file named `hello.txt` inside of it and finally write the string "Hello world!" to it. Let's start with creating the directory:
 
 {{{
@@ -120 +120 @@
 }}}
 
-Finally, we can write our message. This time we use a compound literal to pass our initial position:
+Finally, we can write our string. This time we use a compound literal to pass our initial position:
 
 {{{
-char greeting[] = "Hello world!";
-ssize_t size = vfs_write(hello, (aoff64_t []) {0}, greeting, sizeof(greeting));
+char msg[] = "Hello world!";
+ssize_t size = vfs_write(hello, (aoff64_t []) {0}, msg, sizeof(msg));
 if (size < 0) {
         vfs_put(hello);
@@ -140 +140 @@
 
 Here we are interested in the return code of `vfs_put()` because we made modifications to the file. An error at this point might indicate our data didn't get entirely through.
+
+== Removing a file ==
+
+In general, files may have multiple names - so called hardlinks. To remove one of these hardlinks (including the last one), we must unlink it. We could either use a convenience wrapper (eg. `vfs_unlink_path()`) or, if we already have a file handle of the parent directory and optionally a file handle of the unlinked file, like in the example above, we use `vfs_unlink()`. So imagine we want to remove the file created in the previous example and that neither of `foobar` or `hello` have been put by `vfs_put()` yet:
+
+{{{
+rc = vfs_unlink(parent, "hello", hello);
+if (rc != EOK)
+        return rc;
+}}}
+
+By passing the third argument to `vfs_unlink()` above, we are making sure that we won't accidentally remove some other link called `hello` created by someone else after the original `hello` had been removed. Note that this argument can be -1 if we don't care.