From 4f79dd28d714dbaf225ac5062ca1f2527567a81d Mon Sep 17 00:00:00 2001
From: Sergey Bugaev <bugaevc@gmail.com>
Date: Sat, 8 May 2021 18:31:41 +0300
Subject: libpager: pager_write_page () should not unmap page

Clarify this in the documentation, and fix the storeio implementation.
Message-Id: <20210508153144.332832-2-bugaevc@gmail.com>
---
 doc/hurd.texi       | 6 +++---
 libpager/pager.h    | 6 +++---
 storeio/pager.c     | 8 +++-----
 tmpfs/pager-stubs.c | 6 +++---
 4 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/doc/hurd.texi b/doc/hurd.texi
index f63cfcda..0a38ca77 100644
--- a/doc/hurd.texi
+++ b/doc/hurd.texi
@@ -1536,9 +1536,9 @@ only permissible error returns are @code{EIO}, @code{EDQUOT}, and
 
 @deftypefun error_t pager_write_page (@w{struct user_pager_info *@var{pager}}, @w{vm_offset_t @var{page}}, @w{vm_address_t @var{buf}})
 For pager @var{pager}, synchronously write one page from @var{buf} to
-offset @var{page}.  In addition, @code{vm_deallocate} (or equivalent)
-@var{buf}.  The only permissible error returns are @code{EIO},
-@code{EDQUOT}, and @code{ENOSPC}.
+offset @var{page}.  Do not deallocate @var{buf}, and do not keep any
+references to @var{buf}.  The only permissible error returns are
+@code{EIO}, @code{EDQUOT}, and @code{ENOSPC}.
 @end deftypefun
 
 @deftypefun error_t pager_unlock_page (@w{struct user_pager_info *@var{pager}}, @w{vm_offset_t @var{address}})
diff --git a/libpager/pager.h b/libpager/pager.h
index d2a8d397..dd8026a7 100644
--- a/libpager/pager.h
+++ b/libpager/pager.h
@@ -191,9 +191,9 @@ pager_read_page (struct user_pager_info *pager,
 		 int *write_lock);
 
 /* The user must define this function.  For pager PAGER, synchronously
-   write one page from BUF to offset PAGE.  In addition, mfree
-   (or equivalent) BUF.  The only permissible error returns are EIO,
-   EDQUOT, and ENOSPC. */
+   write one page from BUF to offset PAGE.  Do not deallocate BUF, and do
+   not keep any references to BUF.  The only permissible error returns
+   are EIO, EDQUOT, and ENOSPC. */
 error_t
 pager_write_page (struct user_pager_info *pager,
 		  vm_offset_t page,
diff --git a/storeio/pager.c b/storeio/pager.c
index 12387939..01a1525c 100644
--- a/storeio/pager.c
+++ b/storeio/pager.c
@@ -66,9 +66,9 @@ pager_read_page (struct user_pager_info *upi,
     return 0;
 }
 
-/* For pager PAGER, synchronously write one page from BUF to offset PAGE.  In
-   addition, vm_deallocate (or equivalent) BUF.  The only permissible error
-   returns are EIO, EDQUOT, and ENOSPC. */
+/* For pager PAGER, synchronously write one page from BUF to offset PAGE.
+   Do not deallocate BUF, and do not keep any references to BUF.  The only
+   permissible error returns are EIO, EDQUOT, and ENOSPC. */
 error_t
 pager_write_page (struct user_pager_info *upi,
 		  vm_offset_t page, vm_address_t buf)
@@ -90,8 +90,6 @@ pager_write_page (struct user_pager_info *upi,
 
       err = dev_write (dev, page, (char *)buf, want, &written);
 
-      munmap ((caddr_t) buf, vm_page_size);
-
       if (err || written < want)
 	return EIO;
       else
diff --git a/tmpfs/pager-stubs.c b/tmpfs/pager-stubs.c
index 3299e218..883a635e 100644
--- a/tmpfs/pager-stubs.c
+++ b/tmpfs/pager-stubs.c
@@ -36,9 +36,9 @@ pager_read_page (struct user_pager_info *pager,
 }
 
 /* The user must define this function.  For pager PAGER, synchronously
-   write one page from BUF to offset PAGE.  In addition, mfree
-   (or equivalent) BUF.  The only permissible error returns are EIO,
-   EDQUOT, and ENOSPC. */
+   write one page from BUF to offset PAGE.  Do not deallocate BUF, and do
+   not keep any references to BUF.  The only permissible error returns
+   are EIO, EDQUOT, and ENOSPC. */
 error_t
 pager_write_page (struct user_pager_info *pager,
 		  vm_offset_t page,
-- 
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