implement linkat

kmod/file.c

@@ -899,23 +899,14 @@ static ssize_t file_write_iter(struct kiocb* iocb, struct iov_iter* from) {
     return res;
 }
 
-int ternfs_file_flush(struct ternfs_inode* enode, struct dentry* dentry) {
-    inode_lock(&enode->inode);
+// shared functionality of ternfs_flush and ternfs_link
+// takes the file we're trying to flush/link, the directory we're going to put it in, and a name/len pair to assign
+// note: caller must take care of dget_parent/dput
+static int flush_and_link(struct ternfs_inode *enode, struct dentry *parent, const char *name, size_t name_len) {
+    BUG_ON(!inode_is_locked(&enode->inode));
 
     int err = 0;
 
-    // Not writing, there's nothing to do, there's nothing to do, files are immutable
-    if (enode->file.status != TERNFS_FILE_STATUS_WRITING) {
-        ternfs_debug("status=%d, won't flush", enode->file.status);
-        goto out_early;
-    }
-
-    // We are in another process, skip
-    if (enode->file.owner != current->group_leader) {
-        ternfs_debug("owner=%p != group_leader=%p, won't flush", enode->file.owner, current->group_leader);
-        goto out_early;
-    }
-
     bool file_is_alive_and_flushing = false;
 
     // if we've errored out already, just exit
@@ -948,7 +939,7 @@ int ternfs_file_flush(struct ternfs_inode* enode, struct dentry* dentry) {
     ternfs_debug("linking file");
     err = ternfs_error_to_linux(ternfs_shard_link_file(
         (struct ternfs_fs_info*)enode->inode.i_sb->s_fs_info, enode->inode.i_ino,
-        enode->file.cookie, dentry->d_parent->d_inode->i_ino, dentry->d_name.name, dentry->d_name.len,
+        enode->file.cookie, parent->d_inode->i_ino, name, name_len,
         &enode->edge_creation_time
     ));
     if (err < 0) { goto out; }
@@ -963,11 +954,7 @@ int ternfs_file_flush(struct ternfs_inode* enode, struct dentry* dentry) {
 
     // expire the directory listing -- we know for a fact that it
     // is wrong, it now contains this file.
-    {
-        struct dentry* parent = dget_parent(dentry);
-        WRITE_ONCE(TERNFS_I(d_inode(parent))->dir.mtime_expiry, 0);
-        dput(parent);
-    }
+    WRITE_ONCE(TERNFS_I(d_inode(parent))->dir.mtime_expiry, 0);
 
 out:
     if (err) {
@@ -999,17 +986,89 @@ int ternfs_file_flush(struct ternfs_inode* enode, struct dentry* dentry) {
         mmdrop(enode->file.mm);
     }
     enode->file.mm = NULL;
-    inode_unlock(&enode->inode);
+
     return err;
+}
+
+int ternfs_file_flush(struct ternfs_inode* enode, struct dentry* dentry) {
+    int err = 0;
+    inode_lock(&enode->inode);
+
+    // Not writing, there's nothing to do, there's nothing to do, files are immutable
+    if (enode->file.status != TERNFS_FILE_STATUS_WRITING) {
+        ternfs_debug("status=%d, won't flush", enode->file.status);
+        goto out;
+    }
+
+    // We are in another process, skip
+    if (enode->file.owner != current->group_leader) {
+        ternfs_debug("owner=%p != group_leader=%p, won't flush", enode->file.owner, current->group_leader);
+        goto out;
+    }
 
-out_early:
+
+    struct dentry *parent = dget_parent(dentry);
+
+    err = flush_and_link(enode, parent, dentry->d_name.name, dentry->d_name.len);
+
+    if (parent)
+        dput(parent);
+
+out:
     inode_unlock(&enode->inode);
     return err;
 }
 
+int ternfs_link(struct dentry* old_dentry, struct inode* dir, struct dentry* new_dentry) {
+    struct inode* inode = d_inode(old_dentry);
+    struct ternfs_inode* enode = TERNFS_I(inode);
+
+    // should be done by vfs_link
+    BUG_ON(!inode_is_locked(inode));
+
+    int err = 0;
+
+    struct dentry* parent = dget_parent(old_dentry);
+
+    // TODO: there are probably cases in which this could be allowed (e.g. cross directory things that happen to be in the same shard)
+    if (!parent || parent->d_inode != dir) {
+        ternfs_debug("tried to link a file in a different directory than the one it was opened in");
+        err = -EXDEV;
+        goto out;
+    }
+
+    // linking existing files is not allowed
+    // TODO: check i_nlink once we actually start reporting link counts
+    if (enode->file.status != TERNFS_FILE_STATUS_WRITING) {
+        ternfs_debug("status=%d, won't link", enode->file.status);
+        err = -EINVAL;
+        goto out;
+    }
+
+    // this is not an error in normal flush (because other processes could close the fd) but linking would be weird
+    if (enode->file.owner != current->group_leader) {
+        ternfs_debug("owner=%p != group_leader=%p, won't link", enode->file.owner, current->group_leader);
+        err = -EPERM;
+        goto out;
+    }
+
+    err = flush_and_link(enode, parent, new_dentry->d_name.name, new_dentry->d_name.len);
+
+out:
+    if (parent)
+        dput(parent);
+
+    return err;
+}
+
 static int file_flush_internal(struct file* filp, fl_owner_t id) { // can we get write while this is in progress?
     struct ternfs_inode* enode = TERNFS_I(filp->f_inode);
     struct dentry* dentry = filp->f_path.dentry;
+
+    // ternfs_file_flush also links, but tmpfiles are only linked when linkat is called
+    if (unlikely(filp->f_flags & __O_TMPFILE))
+        return 0;
+
     return ternfs_file_flush(enode, dentry);
 }
 

kmod/file.h

@@ -16,6 +16,7 @@ extern int ternfs_file_getattr_refresh_time_jiffies; // this is only relevant fo
 
 ssize_t ternfs_file_write(struct ternfs_inode* enode, int flags, loff_t* ppos, struct iov_iter* from);
 int ternfs_file_flush(struct ternfs_inode* enode, struct dentry* dentry);
+int ternfs_link(struct dentry* old_dentry, struct inode* dir, struct dentry* new_dentry);
 
 // Also used in ternfs_do_ftruncate to fill the end of the file.
 ssize_t ternfs_file_write_internal(struct ternfs_inode* enode, int flags, loff_t* ppos, struct iov_iter* from, size_t count);

kmod/inode.c

@@ -607,6 +607,30 @@ static int COMPAT_FUNC_UNS_IMP(ternfs_symlink, struct inode* dir, struct dentry*
     return 0;
 }
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(6,6,0)
+static int COMPAT_FUNC_UNS_IMP(ternfs_tmpfile, struct inode* dir, struct file* file, umode_t mode) {
+    struct dentry* dentry = file->f_path.dentry; // dentry with a "fake" name
+#else
+static int COMPAT_FUNC_UNS_IMP(ternfs_tmpfile, struct inode* dir, struct dentry* dentry, umode_t mode) {
+#endif
+    ternfs_debug("ternfs_tempfile: name: %s", dentry->d_name.name);
+    struct ternfs_inode* enode = ternfs_create_internal(dir, TERNFS_INODE_FILE, dentry);
+    if (IS_ERR(enode)) { return PTR_ERR(enode); }
+
+    // the file is created in writing status by ternfs_create_internal
+    // and it remains unlinked until linkat() is called
+    // once link is called we can then assign a name
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(6,6,0)
+    // in 6.6+, finish_open_simple handles d_instantiate
+    return finish_open_simple(file, 0);
+#else
+    // for older kernels, we need to instantiate as unhashed
+    d_tmpfile(dentry, &enode->inode);
+    return 0;
+#endif
+}
+
 static const char* ternfs_get_link(struct dentry* dentry, struct inode* inode, struct delayed_call* destructor) {
     // Can't be bothered to think about RCU
     if (dentry == NULL) { return ERR_PTR(-ECHILD); }
@@ -625,12 +649,14 @@ static const char* ternfs_get_link(struct dentry* dentry, struct inode* inode, s
 static const struct inode_operations ternfs_dir_inode_ops = {
     .create = ternfs_create,
     .lookup = ternfs_lookup,
+    .link = ternfs_link,
     .unlink = ternfs_unlink,
     .mkdir = ternfs_mkdir,
     .rmdir = ternfs_rmdir,
     .rename = ternfs_rename,
     .getattr = ternfs_getattr,
     .symlink = ternfs_symlink,
+    .tmpfile = ternfs_tmpfile,
 };
 
 static const struct inode_operations ternfs_file_inode_ops = {