Linux: Use kernel_read/kernel_write when __vfs variants are unavailable

We hide the uses of set_fs/get_fs behind a macro, as those functions
are likely to soon become unavailable:

> Christoph Hellwig suggested removing all calls outside of the core
> filesystem and architecture code; Andy Lutomirski went one step
> further and said they should all go.

    https://lwn.net/Articles/722267/

Change-Id: Ib668f8fdb62ca01fe14321c07bd14d218744d909
Reviewed-on: https://gerrit.openafs.org/12729
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>

diff --git a/acinclude.m4 b/acinclude.m4
index 162a3e9..703d3ea 100644 (file)
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -1004,6 +1004,9 @@ case $AFS_SYSNAME in *_linux* | *_umlinux*)
                 AC_CHECK_LINUX_FUNC([__vfs_write],
                                     [#include <linux/fs.h>],
                                     [__vfs_write(NULL, NULL, 0, NULL);])
+                AC_CHECK_LINUX_FUNC([kernel_write],
+                                    [#include <linux/fs.h>],
+                                    [kernel_write(NULL, NULL, 0, NULL);])
                  AC_CHECK_LINUX_FUNC([bdi_init],
                                     [#include <linux/backing-dev.h>],
                                     [bdi_init(NULL);])

diff --git a/src/afs/LINUX/osi_compat.h b/src/afs/LINUX/osi_compat.h
index 13915b9..60cfdc1 100644 (file)
--- a/src/afs/LINUX/osi_compat.h
+++ b/src/afs/LINUX/osi_compat.h
@@ -645,11 +645,21 @@ afs_d_invalidate(struct dentry *dp)
 #endif
 }
 
+#if defined(HAVE_LINUX___VFS_WRITE)
+# define AFS_FILE_NEEDS_SET_FS 1
+#elif defined(HAVE_LINUX_KERNEL_WRITE)
+/* #undef AFS_FILE_NEEDS_SET_FS */
+#else
+# define AFS_FILE_NEEDS_SET_FS 1
+#endif
+
 static inline int
 afs_file_read(struct file *filp, char __user *buf, size_t len, loff_t *pos)
 {
 #if defined(HAVE_LINUX___VFS_WRITE)
     return __vfs_read(filp, buf, len, pos);
+#elif defined(HAVE_LINUX_KERNEL_WRITE)
+    return kernel_read(filp, buf, len, pos);
 #else
     return filp->f_op->read(filp, buf, len, pos);
 #endif
@@ -660,6 +670,8 @@ afs_file_write(struct file *filp, char __user *buf, size_t len, loff_t *pos)
 {
 #if defined(HAVE_LINUX___VFS_WRITE)
     return __vfs_write(filp, buf, len, pos);
+#elif defined(HAVE_LINUX_KERNEL_WRITE)
+    return kernel_write(filp, buf, len, pos);
 #else
     return filp->f_op->write(filp, buf, len, pos);
 #endif

diff --git a/src/afs/LINUX/osi_file.c b/src/afs/LINUX/osi_file.c
index 1718c96..0374c1c 100644 (file)
--- a/src/afs/LINUX/osi_file.c
+++ b/src/afs/LINUX/osi_file.c
@@ -356,7 +356,9 @@ int
 osi_rdwr(struct osi_file *osifile, struct uio *uiop, int rw)
 {
     struct file *filp = osifile->filp;
+#ifdef AFS_FILE_NEEDS_SET_FS
     mm_segment_t old_fs = {0};
+#endif /* AFS_FILE_NEEDS_SET_FS */
     int code = 0;
     struct iovec *iov;
     size_t count;
@@ -366,11 +368,13 @@ osi_rdwr(struct osi_file *osifile, struct uio *uiop, int rw)
     savelim = current->TASK_STRUCT_RLIM[RLIMIT_FSIZE].rlim_cur;
     current->TASK_STRUCT_RLIM[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
 
+#ifdef AFS_FILE_NEEDS_SET_FS
     if (uiop->uio_seg == AFS_UIOSYS) {
        /* Switch into user space */
        old_fs = get_fs();
        set_fs(get_ds());
     }
+#endif /* AFS_FILE_NEEDS_SET_FS */
 
     while (code == 0 && uiop->uio_resid > 0 && uiop->uio_iovcnt > 0) {
        iov = uiop->uio_iov;
@@ -407,10 +411,12 @@ osi_rdwr(struct osi_file *osifile, struct uio *uiop, int rw)
        code = 0;
     }
 
+#ifdef AFS_FILE_NEEDS_SET_FS
     if (uiop->uio_seg == AFS_UIOSYS) {
        /* Switch back into kernel space */
        set_fs(old_fs);
     }
+#endif /* AFS_FILE_NEEDS_SET_FS */
 
     current->TASK_STRUCT_RLIM[RLIMIT_FSIZE].rlim_cur = savelim;
 

diff --git a/src/afs/LINUX/osi_vnodeops.c b/src/afs/LINUX/osi_vnodeops.c
index d935cf5..b7e4734 100644 (file)
--- a/src/afs/LINUX/osi_vnodeops.c
+++ b/src/afs/LINUX/osi_vnodeops.c
@@ -825,7 +825,7 @@ struct file_operations afs_file_fops = {
 #ifdef STRUCT_FILE_OPERATIONS_HAS_READ_ITER
   .read_iter = afs_linux_read_iter,
   .write_iter =        afs_linux_write_iter,
-# if !defined(HAVE_LINUX___VFS_WRITE)
+# if !defined(HAVE_LINUX___VFS_WRITE) && !defined(HAVE_LINUX_KERNEL_WRITE)
   .read =      new_sync_read,
   .write =     new_sync_write,
 # endif