ANDROID: fs: Add read_comp_algo_dictionary() to read compression dictionaries

Partner zram driver reads a file to populate its compression dictionary.
To support this while restricting kernel_read_file_from_path() usage,
introduce read_comp_algo_dictionary().

This function wraps kernel_read_file_from_path() and is GPL-exported.
It allows zram and similar users to load dictionaries while keeping
direct usage of kernel_read_file_from_path() controlled.

Bug: 407663651
Change-Id: I013330e270dc6a7529e83ef4efc1472c198fcc92
Signed-off-by: Donghyeok Choe <d7271.choe@samsung.com>
(cherry picked from commit b9f02b7e52)
(cherry picked from commit f1485e6d19010d5b17062c1adbec437086e2b75f)

fs/kernel_read_file.c

@@ -183,3 +183,13 @@ ssize_t kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
 	return kernel_read_file(fd_file(f), offset, buf, buf_size, file_size, id);
 }
 EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);
+
+ssize_t read_comp_algo_dictionary(void **dict, const char *dict_path)
+{
+	return kernel_read_file_from_path(dict_path, 0,
+					  dict,
+					  INT_MAX,
+					  NULL,
+					  READING_POLICY);
+}
+EXPORT_SYMBOL_GPL(read_comp_algo_dictionary);

include/linux/kernel_read_file.h

@@ -53,4 +53,6 @@ ssize_t kernel_read_file_from_fd(int fd, loff_t offset,
 				 size_t *file_size,
 				 enum kernel_read_file_id id);
 
+ssize_t read_comp_algo_dictionary(void **dict, const char *dict_path);
+
 #endif /* _LINUX_KERNEL_READ_FILE_H */