[RFC PATCH v1 03/10] lib: extract freader into a separate files

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

From: Mykyta Yatsenko <yatsenko@meta.com>

Move the freader implementation from buildid.{c,h} into a dedicated
compilation unit, freader.{c,h}.

This allows reuse of freader outside buildid, e.g. for file dynptr
support added later. Includes are updated and symbols are exported as
needed. No functional change intended.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 include/linux/freader.h |  32 +++++++++
 lib/Makefile            |   2 +-
 lib/buildid.c           | 145 +---------------------------------------
 lib/freader.c           | 133 ++++++++++++++++++++++++++++++++++++
 4 files changed, 167 insertions(+), 145 deletions(-)
 create mode 100644 include/linux/freader.h
 create mode 100644 lib/freader.c

diff --git a/include/linux/freader.h b/include/linux/freader.h
new file mode 100644
index 000000000000..a08ea9f59945
--- /dev/null
+++ b/include/linux/freader.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_FREADER_H
+#define _LINUX_FREADER_H
+
+#include <linux/types.h>
+
+struct freader {
+	void *buf;
+	u32 buf_sz;
+	int err;
+	union {
+		struct {
+			struct file *file;
+			struct folio *folio;
+			void *addr;
+			loff_t folio_off;
+			bool may_fault;
+		};
+		struct {
+			const char *data;
+			u64 data_sz;
+		};
+	};
+};
+
+void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz,
+			    struct file *file, bool may_fault);
+void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz);
+const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz);
+void freader_cleanup(struct freader *r);
+int freader_err(struct freader *r);
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index 392ff808c9b9..4761885228fa 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -40,7 +40,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
 	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
 	 nmi_backtrace.o win_minmax.o memcat_p.o \
-	 buildid.o objpool.o iomem_copy.o sys_info.o
+	 buildid.o objpool.o iomem_copy.o sys_info.o freader.o
 
 lib-$(CONFIG_UNION_FIND) += union_find.o
 lib-$(CONFIG_PRINTK) += dump_stack.o
diff --git a/lib/buildid.c b/lib/buildid.c
index c4b0f376fb34..e770dc4b73d3 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -6,155 +6,12 @@
 #include <linux/kernel.h>
 #include <linux/pagemap.h>
 #include <linux/secretmem.h>
+#include <linux/freader.h>
 
 #define BUILD_ID 3
 
 #define MAX_PHDR_CNT 256
 
-struct freader {
-	void *buf;
-	u32 buf_sz;
-	int err;
-	union {
-		struct {
-			struct file *file;
-			struct folio *folio;
-			void *addr;
-			loff_t folio_off;
-			bool may_fault;
-		};
-		struct {
-			const char *data;
-			u64 data_sz;
-		};
-	};
-};
-
-static void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz,
-				   struct file *file, bool may_fault)
-{
-	memset(r, 0, sizeof(*r));
-	r->buf = buf;
-	r->buf_sz = buf_sz;
-	r->file = file;
-	r->may_fault = may_fault;
-}
-
-static void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz)
-{
-	memset(r, 0, sizeof(*r));
-	r->data = data;
-	r->data_sz = data_sz;
-}
-
-static void freader_put_folio(struct freader *r)
-{
-	if (!r->folio)
-		return;
-	kunmap_local(r->addr);
-	folio_put(r->folio);
-	r->folio = NULL;
-}
-
-static int freader_get_folio(struct freader *r, loff_t file_off)
-{
-	/* check if we can just reuse current folio */
-	if (r->folio && file_off >= r->folio_off &&
-	    file_off < r->folio_off + folio_size(r->folio))
-		return 0;
-
-	freader_put_folio(r);
-
-	/* reject secretmem folios created with memfd_secret() */
-	if (secretmem_mapping(r->file->f_mapping))
-		return -EFAULT;
-
-	r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
-
-	/* if sleeping is allowed, wait for the page, if necessary */
-	if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) {
-		filemap_invalidate_lock_shared(r->file->f_mapping);
-		r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT,
-					    NULL, r->file);
-		filemap_invalidate_unlock_shared(r->file->f_mapping);
-	}
-
-	if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) {
-		if (!IS_ERR(r->folio))
-			folio_put(r->folio);
-		r->folio = NULL;
-		return -EFAULT;
-	}
-
-	r->folio_off = folio_pos(r->folio);
-	r->addr = kmap_local_folio(r->folio, 0);
-
-	return 0;
-}
-
-static const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz)
-{
-	size_t folio_sz;
-
-	/* provided internal temporary buffer should be sized correctly */
-	if (WARN_ON(r->buf && sz > r->buf_sz)) {
-		r->err = -E2BIG;
-		return NULL;
-	}
-
-	if (unlikely(file_off + sz < file_off)) {
-		r->err = -EOVERFLOW;
-		return NULL;
-	}
-
-	/* working with memory buffer is much more straightforward */
-	if (!r->buf) {
-		if (file_off + sz > r->data_sz) {
-			r->err = -ERANGE;
-			return NULL;
-		}
-		return r->data + file_off;
-	}
-
-	/* fetch or reuse folio for given file offset */
-	r->err = freader_get_folio(r, file_off);
-	if (r->err)
-		return NULL;
-
-	/* if requested data is crossing folio boundaries, we have to copy
-	 * everything into our local buffer to keep a simple linear memory
-	 * access interface
-	 */
-	folio_sz = folio_size(r->folio);
-	if (file_off + sz > r->folio_off + folio_sz) {
-		int part_sz = r->folio_off + folio_sz - file_off;
-
-		/* copy the part that resides in the current folio */
-		memcpy(r->buf, r->addr + (file_off - r->folio_off), part_sz);
-
-		/* fetch next folio */
-		r->err = freader_get_folio(r, r->folio_off + folio_sz);
-		if (r->err)
-			return NULL;
-
-		/* copy the rest of requested data */
-		memcpy(r->buf + part_sz, r->addr, sz - part_sz);
-
-		return r->buf;
-	}
-
-	/* if data fits in a single folio, just return direct pointer */
-	return r->addr + (file_off - r->folio_off);
-}
-
-static void freader_cleanup(struct freader *r)
-{
-	if (!r->buf)
-		return; /* non-file-backed mode */
-
-	freader_put_folio(r);
-}
-
 /*
  * Parse build id from the note segment. This logic can be shared between
  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
diff --git a/lib/freader.c b/lib/freader.c
new file mode 100644
index 000000000000..32a17d137b32
--- /dev/null
+++ b/lib/freader.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/freader.h>
+#include <linux/cache.h>
+#include <linux/elf.h>
+#include <linux/kernel.h>
+#include <linux/pagemap.h>
+#include <linux/secretmem.h>
+
+void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz,
+			    struct file *file, bool may_fault)
+{
+	memset(r, 0, sizeof(*r));
+	r->buf = buf;
+	r->buf_sz = buf_sz;
+	r->file = file;
+	r->may_fault = may_fault;
+}
+
+void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz)
+{
+	memset(r, 0, sizeof(*r));
+	r->data = data;
+	r->data_sz = data_sz;
+}
+
+static void freader_put_folio(struct freader *r)
+{
+	if (!r->folio)
+		return;
+	kunmap_local(r->addr);
+	folio_put(r->folio);
+	r->folio = NULL;
+}
+
+static int freader_get_folio(struct freader *r, loff_t file_off)
+{
+	/* check if we can just reuse current folio */
+	if (r->folio && file_off >= r->folio_off &&
+	    file_off < r->folio_off + folio_size(r->folio))
+		return 0;
+
+	freader_put_folio(r);
+
+	/* reject secretmem folios created with memfd_secret() */
+	if (secretmem_mapping(r->file->f_mapping))
+		return -EFAULT;
+
+	r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
+
+	/* if sleeping is allowed, wait for the page, if necessary */
+	if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) {
+		filemap_invalidate_lock_shared(r->file->f_mapping);
+		r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT,
+					    NULL, r->file);
+		filemap_invalidate_unlock_shared(r->file->f_mapping);
+	}
+
+	if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) {
+		if (!IS_ERR(r->folio))
+			folio_put(r->folio);
+		r->folio = NULL;
+		return -EFAULT;
+	}
+
+	r->folio_off = folio_pos(r->folio);
+	r->addr = kmap_local_folio(r->folio, 0);
+
+	return 0;
+}
+
+const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz)
+{
+	size_t folio_sz;
+
+	/* provided internal temporary buffer should be sized correctly */
+	if (WARN_ON(r->buf && sz > r->buf_sz)) {
+		r->err = -E2BIG;
+		return NULL;
+	}
+
+	if (unlikely(file_off + sz < file_off)) {
+		r->err = -EOVERFLOW;
+		return NULL;
+	}
+
+	/* working with memory buffer is much more straightforward */
+	if (!r->buf) {
+		if (file_off + sz > r->data_sz) {
+			r->err = -ERANGE;
+			return NULL;
+		}
+		return r->data + file_off;
+	}
+
+	/* fetch or reuse folio for given file offset */
+	r->err = freader_get_folio(r, file_off);
+	if (r->err)
+		return NULL;
+
+	/* if requested data is crossing folio boundaries, we have to copy
+	 * everything into our local buffer to keep a simple linear memory
+	 * access interface
+	 */
+	folio_sz = folio_size(r->folio);
+	if (file_off + sz > r->folio_off + folio_sz) {
+		int part_sz = r->folio_off + folio_sz - file_off;
+
+		/* copy the part that resides in the current folio */
+		memcpy(r->buf, r->addr + (file_off - r->folio_off), part_sz);
+
+		/* fetch next folio */
+		r->err = freader_get_folio(r, r->folio_off + folio_sz);
+		if (r->err)
+			return NULL;
+
+		/* copy the rest of requested data */
+		memcpy(r->buf + part_sz, r->addr, sz - part_sz);
+
+		return r->buf;
+	}
+
+	/* if data fits in a single folio, just return direct pointer */
+	return r->addr + (file_off - r->folio_off);
+}
+
+void freader_cleanup(struct freader *r)
+{
+	if (!r->buf)
+		return; /* non-file-backed mode */
+
+	freader_put_folio(r);
+}
-- 
2.51.0