switch generic_write_checks() to iocb and iter

... returning -E... upon error and amount of data left in iter after
(possible) truncation upon success.  Note, that normal case gives
a non-zero (positive) return value, so any tests for != 0 _must_ be
updated.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Conflicts:
	fs/ext4/file.c

14 files changed, 99 insertions, 166 deletions

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index b5b020ace1b3..2a9dd37dc426 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -404,21 +404,16 @@ static ssize_t
 v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
         struct file *file = iocb->ki_filp;
-        ssize_t retval = 0;
-        loff_t origin = iocb->ki_pos;
-        size_t count = iov_iter_count(from);
+        ssize_t retval;
+        loff_t origin;
         int err = 0;
 
-        retval = generic_write_checks(file, &origin, &count);
-        if (retval)
+        retval = generic_write_checks(iocb, from);
+        if (retval <= 0)
                 return retval;
 
-        iov_iter_truncate(from, count);
-
-        if (!count)
-                return 0;
-
-        retval = p9_client_write(file->private_data, origin, from, &err);
+        origin = iocb->ki_pos;
+        retval = p9_client_write(file->private_data, iocb->ki_pos, from, &err);
         if (retval > 0) {
                 struct inode *inode = file_inode(file);
                 loff_t i_size;
@@ -428,12 +423,11 @@ v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
                 if (inode->i_mapping && inode->i_mapping->nrpages)
                         invalidate_inode_pages2_range(inode->i_mapping,
                                                       pg_start, pg_end);
-                origin += retval;
+                iocb->ki_pos += retval;
                 i_size = i_size_read(inode);
-                iocb->ki_pos = origin;
-                if (origin > i_size) {
-                        inode_add_bytes(inode, origin - i_size);
-                        i_size_write(inode, origin);
+                if (iocb->ki_pos > i_size) {
+                        inode_add_bytes(inode, iocb->ki_pos - i_size);
+                        i_size_write(inode, iocb->ki_pos);
                 }
                 return retval;
         }
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 691a84a81e09..c64d11c41eeb 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1739,27 +1739,19 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
         u64 start_pos;
         u64 end_pos;
         ssize_t num_written = 0;
-        ssize_t err = 0;
-        size_t count = iov_iter_count(from);
         bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
-        loff_t pos = iocb->ki_pos;
+        ssize_t err;
+        loff_t pos;
+        size_t count;
 
         mutex_lock(&inode->i_mutex);
-
-        current->backing_dev_info = inode_to_bdi(inode);
-        err = generic_write_checks(file, &pos, &count);
-        if (err) {
+        err = generic_write_checks(iocb, from);
+        if (err <= 0) {
                 mutex_unlock(&inode->i_mutex);
-                goto out;
-        }
-
-        if (count == 0) {
-                mutex_unlock(&inode->i_mutex);
-                goto out;
+                return err;
         }
 
-        iov_iter_truncate(from, count);
-
+        current->backing_dev_info = inode_to_bdi(inode);
         err = file_remove_suid(file);
         if (err) {
                 mutex_unlock(&inode->i_mutex);
@@ -1786,6 +1778,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
          */
         update_time_for_write(inode);
 
+        pos = iocb->ki_pos;
+        count = iov_iter_count(from);
         start_pos = round_down(pos, root->sectorsize);
         if (start_pos > i_size_read(inode)) {
                 /* Expand hole size to cover write data, preventing empty gap */
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 761841903160..3f0b9339d823 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -941,9 +941,9 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
         struct ceph_inode_info *ci = ceph_inode(inode);
         struct ceph_osd_client *osdc =
                 &ceph_sb_to_client(inode->i_sb)->client->osdc;
-        ssize_t count = iov_iter_count(from), written = 0;
+        ssize_t count, written = 0;
         int err, want, got;
-        loff_t pos = iocb->ki_pos;
+        loff_t pos;
 
         if (ceph_snap(inode) != CEPH_NOSNAP)
                 return -EROFS;
@@ -953,14 +953,12 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
         /* We can write back this queue in page reclaim */
         current->backing_dev_info = inode_to_bdi(inode);
 
-        err = generic_write_checks(file, &pos, &count);
-        if (err)
-                goto out;
-
-        if (count == 0)
+        err = generic_write_checks(iocb, from);
+        if (err <= 0)
                 goto out;
-        iov_iter_truncate(from, count);
 
+        pos = iocb->ki_pos;
+        count = iov_iter_count(from);
         err = file_remove_suid(file);
         if (err)
                 goto out;
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 4202e74b2db5..ca2bc5406306 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2563,7 +2563,6 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
 ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
 {
         struct file *file = iocb->ki_filp;
-        size_t len;
         ssize_t total_written = 0;
         struct cifsFileInfo *open_file;
         struct cifs_tcon *tcon;
@@ -2579,16 +2578,10 @@ ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
          * write request.
          */
 
-        len = iov_iter_count(from);
-        rc = generic_write_checks(file, &iocb->ki_pos, &len);
-        if (rc)
+        rc = generic_write_checks(iocb, from);
+        if (rc <= 0)
                 return rc;
 
-        if (!len)
-                return 0;
-
-        iov_iter_truncate(from, len);
-
         INIT_LIST_HEAD(&wdata_list);
         cifs_sb = CIFS_FILE_SB(file);
         open_file = file->private_data;
@@ -2599,8 +2592,8 @@ ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
 
         memcpy(&saved_from, from, sizeof(struct iov_iter));
 
-        rc = cifs_write_from_iter(iocb->ki_pos, len, from, open_file, cifs_sb,
-                                  &wdata_list);
+        rc = cifs_write_from_iter(iocb->ki_pos, iov_iter_count(from), from,
+                                  open_file, cifs_sb, &wdata_list);
 
         /*
          * If at least one write was successfully sent, then discard any rc
@@ -2674,7 +2667,6 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from)
         struct cifsInodeInfo *cinode = CIFS_I(inode);
         struct TCP_Server_Info *server = tlink_tcon(cfile->tlink)->ses->server;
         ssize_t rc;
-        size_t count;
 
         /*
          * We need to hold the sem to be sure nobody modifies lock list
@@ -2683,16 +2675,10 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from)
         down_read(&cinode->lock_sem);
         mutex_lock(&inode->i_mutex);
 
-        count = iov_iter_count(from);
-        rc = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (rc)
+        rc = generic_write_checks(iocb, from);
+        if (rc <= 0)
                 goto out;
 
-        if (count == 0)
-                goto out;
-
-        iov_iter_truncate(from, count);
-
         if (!cifs_find_lock_conflict(cfile, iocb->ki_pos, iov_iter_count(from),
                                      server->vals->exclusive_lock_type, NULL,
                                      CIFS_WRITE_OP))
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 42b1fa33a17a..c10785f10d1d 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -97,9 +97,7 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         struct blk_plug plug;
         int o_direct = io_is_direct(file);
         int overwrite = 0;
-        size_t length = iov_iter_count(from);
         ssize_t ret;
-        loff_t pos;
 
         /*
          * Unaligned direct AIO must be serialized; see comment above
@@ -116,16 +114,10 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         }
 
         mutex_lock(&inode->i_mutex);
-        ret = generic_write_checks(file, &iocb->ki_pos, &length);
-        if (ret)
+        ret = generic_write_checks(iocb, from);
+        if (ret <= 0)
                 goto out;
 
-        if (length == 0)
-                goto out;
-
-        iov_iter_truncate(from, length);
-        pos = iocb->ki_pos;
-
         /*
          * If we have encountered a bitmap-format file, the size limit
          * is smaller than s_maxbytes, which is for extent-mapped files.
@@ -133,19 +125,19 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
                 struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
-                if (pos >= sbi->s_bitmap_maxbytes) {
+                if (iocb->ki_pos >= sbi->s_bitmap_maxbytes) {
                         ret = -EFBIG;
                         goto out;
                 }
-                iov_iter_truncate(from, sbi->s_bitmap_maxbytes - pos);
+                iov_iter_truncate(from, sbi->s_bitmap_maxbytes - iocb->ki_pos);
         }
 
         iocb->private = &overwrite;
         if (o_direct) {
-                length = iov_iter_count(from);
+                size_t length = iov_iter_count(from);
+                loff_t pos = iocb->ki_pos;
                 blk_start_plug(&plug);
 
-
                 /* check whether we do a DIO overwrite or not */
                 if (ext4_should_dioread_nolock(inode) && !aio_mutex &&
                     !file->f_mapping->nrpages && pos + length <= i_size_read(inode)) {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 8c15d0a077e8..b86c8e08399a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1145,13 +1145,11 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
-        size_t count = iov_iter_count(from);
         ssize_t written = 0;
         ssize_t written_buffered = 0;
         struct inode *inode = mapping->host;
         ssize_t err;
         loff_t endbyte = 0;
-        loff_t pos = iocb->ki_pos;
 
         if (get_fuse_conn(inode)->writeback_cache) {
                 /* Update size (EOF optimization) and mode (SUID clearing) */
@@ -1167,14 +1165,10 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         /* We can write back this queue in page reclaim */
         current->backing_dev_info = inode_to_bdi(inode);
 
-        err = generic_write_checks(file, &pos, &count);
-        if (err)
-                goto out;
-
-        if (count == 0)
+        err = generic_write_checks(iocb, from);
+        if (err <= 0)
                 goto out;
 
-        iov_iter_truncate(from, count);
         err = file_remove_suid(file);
         if (err)
                 goto out;
@@ -1184,6 +1178,7 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
                 goto out;
 
         if (file->f_flags & O_DIRECT) {
+                loff_t pos = iocb->ki_pos;
                 written = generic_file_direct_write(iocb, from, pos);
                 if (written < 0 || !iov_iter_count(from))
                         goto out;
@@ -1209,9 +1204,9 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
                 written += written_buffered;
                 iocb->ki_pos = pos + written_buffered;
         } else {
-                written = fuse_perform_write(file, mapping, from, pos);
+                written = fuse_perform_write(file, mapping, from, iocb->ki_pos);
                 if (written >= 0)
-                        iocb->ki_pos = pos + written;
+                        iocb->ki_pos += written;
         }
 out:
         current->backing_dev_info = NULL;
@@ -1412,7 +1407,6 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
         struct file *file = iocb->ki_filp;
         struct inode *inode = file_inode(file);
         struct fuse_io_priv io = { .async = 0, .file = file };
-        size_t count = iov_iter_count(from);
         ssize_t res;
 
         if (is_bad_inode(inode))
@@ -1420,11 +1414,9 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
 
         /* Don't allow parallel writes to the same file */
         mutex_lock(&inode->i_mutex);
-        res = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (!res) {
-                iov_iter_truncate(from, count);
+        res = generic_write_checks(iocb, from);
+        if (res > 0)
                 res = fuse_direct_io(&io, from, &iocb->ki_pos, FUSE_DIO_WRITE);
-        }
         fuse_invalidate_attr(inode);
         if (res > 0)
                 fuse_write_update_size(inode, iocb->ki_pos);
diff --git a/fs/ncpfs/file.c b/fs/ncpfs/file.c
index ab6363b16556..011324ce9df2 100644
--- a/fs/ncpfs/file.c
+++ b/fs/ncpfs/file.c
@@ -170,20 +170,15 @@ ncp_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         struct file *file = iocb->ki_filp;
         struct inode *inode = file_inode(file);
         size_t already_written = 0;
-        loff_t pos = iocb->ki_pos;
-        size_t count = iov_iter_count(from);
         size_t bufsize;
         int errno;
         void *bouncebuffer;
+        off_t pos;
 
         ncp_dbg(1, "enter %pD2\n", file);
-        errno = generic_write_checks(file, &pos, &count);
-        if (errno)
+        errno = generic_write_checks(iocb, from);
+        if (errno <= 0)
                 return errno;
-        iov_iter_truncate(from, count);
-        
-        if (!count)
-                return 0;
 
         errno = ncp_make_open(inode, O_WRONLY);
         if (errno) {
@@ -201,10 +196,11 @@ ncp_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
                 errno = -EIO;   /* -ENOMEM */
                 goto outrel;
         }
+        pos = iocb->ki_pos;
         while (iov_iter_count(from)) {
                 int written_this_time;
                 size_t to_write = min_t(size_t,
-                                      bufsize - ((off_t)pos % bufsize),
+                                      bufsize - (pos % bufsize),
                                       iov_iter_count(from));
 
                 if (copy_from_iter(bouncebuffer, to_write, from) != to_write) {
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 5ddd77acb3f7..9634189b8545 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -969,24 +969,19 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter,
         struct nfs_direct_req *dreq;
         struct nfs_lock_context *l_ctx;
         loff_t end;
-        size_t count = iov_iter_count(iter);
-        end = (pos + count - 1) >> PAGE_CACHE_SHIFT;
-
-        nfs_add_stats(mapping->host, NFSIOS_DIRECTWRITTENBYTES, count);
 
         dfprintk(FILE, "NFS: direct write(%pD2, %zd@%Ld)\n",
-                file, count, (long long) pos);
+                file, iov_iter_count(iter), (long long) iocb->ki_pos);
 
-        result = generic_write_checks(file, &pos, &count);
-        if (result)
+        result = generic_write_checks(iocb, iter);
+        if (result <= 0)
                 goto out;
 
-        result = -EINVAL;
-        if ((ssize_t) count < 0)
-                goto out;
-        result = 0;
-        if (!count)
-                goto out;
+        nfs_add_stats(mapping->host, NFSIOS_DIRECTWRITTENBYTES,
+                      iov_iter_count(iter));
+
+        pos = iocb->ki_pos;
+        end = (pos + iov_iter_count(iter) - 1) >> PAGE_CACHE_SHIFT;
 
         mutex_lock(&inode->i_mutex);
 
@@ -1001,7 +996,7 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter,
                         goto out_unlock;
         }
 
-        task_io_account_write(count);
+        task_io_account_write(iov_iter_count(iter));
 
         result = -ENOMEM;
         dreq = nfs_direct_req_alloc();
@@ -1009,7 +1004,7 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter,
                 goto out_unlock;
 
         dreq->inode = inode;
-        dreq->bytes_left = count;
+        dreq->bytes_left = iov_iter_count(iter);
         dreq->io_start = pos;
         dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
         l_ctx = nfs_get_lock_context(dreq->ctx);
diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index cec4ec3c1ede..7bb487e663b4 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -339,17 +339,14 @@ static ssize_t ntfs_prepare_file_for_write(struct kiocb *iocb,
         struct inode *vi = file_inode(file);
         ntfs_inode *base_ni, *ni = NTFS_I(vi);
         ntfs_volume *vol = ni->vol;
-        size_t count = iov_iter_count(from);
 
         ntfs_debug("Entering for i_ino 0x%lx, attribute type 0x%x, pos "
                         "0x%llx, count 0x%zx.", vi->i_ino,
                         (unsigned)le32_to_cpu(ni->type),
-                        (unsigned long long)iocb->ki_pos, count);
-        err = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (unlikely(err))
-                goto out;
-        iov_iter_truncate(from, count);
-        if (count == 0)
+                        (unsigned long long)iocb->ki_pos,
+                        iov_iter_count(from));
+        err = generic_write_checks(iocb, from);
+        if (unlikely(err <= 0))
                 goto out;
         /*
          * All checks have passed.  Before we start doing any writing we want
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index fc53ff065364..b93919f50f0f 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2250,9 +2250,10 @@ out:
 static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
                                     struct iov_iter *from)
 {
-        int ret, direct_io, appending, rw_level, have_alloc_sem  = 0;
+        int direct_io, appending, rw_level, have_alloc_sem  = 0;
         int can_do_direct, has_refcount = 0;
         ssize_t written = 0;
+        ssize_t ret;
         size_t count = iov_iter_count(from), orig_count;
         loff_t old_size;
         u32 old_clusters;
@@ -2319,13 +2320,14 @@ relock:
                 ocfs2_inode_unlock(inode, 1);
         }
 
-        orig_count = count;
-        ret = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (ret < 0) {
-                mlog_errno(ret);
+        orig_count = iov_iter_count(from);
+        ret = generic_write_checks(iocb, from);
+        if (ret <= 0) {
+                if (ret)
+                        mlog_errno(ret);
                 goto out;
         }
-        iov_iter_truncate(from, count);
+        count = ret;
 
         can_do_direct = direct_io;
         ret = ocfs2_prepare_inode_for_write(file, iocb->ki_pos, count, appending,
@@ -2349,7 +2351,7 @@ relock:
                 rw_level = -1;
 
                 direct_io = 0;
-                iov_iter_reexpand(from, count = orig_count);
+                iov_iter_reexpand(from, orig_count);
                 goto relock;
         }
 
@@ -2377,7 +2379,7 @@ relock:
                 loff_t endbyte;
                 ssize_t written_buffered;
                 written = generic_file_direct_write(iocb, from, iocb->ki_pos);
-                if (written < 0 || written == count) {
+                if (written < 0 || !iov_iter_count(from)) {
                         ret = written;
                         goto out_dio;
                 }
@@ -2385,7 +2387,6 @@ relock:
                 /*
                  * for completing the rest of the request.
                  */
-                count -= written;
                 written_buffered = generic_perform_write(file, from, iocb->ki_pos);
                 /*
                  * If generic_file_buffered_write() returned a synchronous error
diff --git a/fs/udf/file.c b/fs/udf/file.c
index ccab8b78e363..3de2edafff73 100644
--- a/fs/udf/file.c
+++ b/fs/udf/file.c
@@ -120,21 +120,15 @@ static ssize_t udf_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         ssize_t retval;
         struct file *file = iocb->ki_filp;
         struct inode *inode = file_inode(file);
-        size_t count = iov_iter_count(from);
         struct udf_inode_info *iinfo = UDF_I(inode);
         int err;
 
         mutex_lock(&inode->i_mutex);
 
-        retval = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (retval)
+        retval = generic_write_checks(iocb, from);
+        if (retval <= 0)
                 goto out;
 
-        if (count == 0)
-                goto out;
-
-        iov_iter_truncate(from, count);
-
         down_write(&iinfo->i_data_sem);
         if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
                 loff_t end = iocb->ki_pos + iov_iter_count(from);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index ebde43e15dd9..28d157807b42 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -551,12 +551,12 @@ xfs_file_aio_write_checks(
         struct file             *file = iocb->ki_filp;
         struct inode            *inode = file->f_mapping->host;
         struct xfs_inode        *ip = XFS_I(inode);
-        int                     error = 0;
+        ssize_t                 error = 0;
         size_t                  count = iov_iter_count(from);
 
 restart:
-        error = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (error)
+        error = generic_write_checks(iocb, from);
+        if (error <= 0)
                 return error;
 
         error = xfs_break_layouts(inode, iolock);
@@ -577,13 +577,13 @@ restart:
                         xfs_rw_iunlock(ip, *iolock);
                         *iolock = XFS_IOLOCK_EXCL;
                         xfs_rw_ilock(ip, *iolock);
+                        iov_iter_reexpand(from, count);
                         goto restart;
                 }
                 error = xfs_zero_eof(ip, iocb->ki_pos, i_size_read(inode), &zero);
                 if (error)
                         return error;
         }
-        iov_iter_truncate(from, count);
 
         /*
          * Updating the timestamps will grab the ilock again from
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c7b21db7782f..b4aa400ac723 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2566,7 +2566,7 @@ extern int sb_min_blocksize(struct super_block *, int);
 
 extern int generic_file_mmap(struct file *, struct vm_area_struct *);
 extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
-int generic_write_checks(struct file *file, loff_t *pos, size_t *count);
+extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
diff --git a/mm/filemap.c b/mm/filemap.c
index dfc573c6ec25..243997a26e7c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2260,36 +2260,38 @@ EXPORT_SYMBOL(read_cache_page_gfp);
  * Returns appropriate error code that caller should return or
  * zero in case that write should be allowed.
  */
-inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count)
+inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 {
+        struct file *file = iocb->ki_filp;
         struct inode *inode = file->f_mapping->host;
         unsigned long limit = rlimit(RLIMIT_FSIZE);
+        loff_t pos;
 
-        if (unlikely(*pos < 0))
-                return -EINVAL;
+        if (!iov_iter_count(from))
+                return 0;
 
         /* FIXME: this is for backwards compatibility with 2.4 */
         if (file->f_flags & O_APPEND)
-                *pos = i_size_read(inode);
+                iocb->ki_pos = i_size_read(inode);
+
+        pos = iocb->ki_pos;
 
         if (limit != RLIM_INFINITY) {
-                if (*pos >= limit) {
+                if (iocb->ki_pos >= limit) {
                         send_sig(SIGXFSZ, current, 0);
                         return -EFBIG;
                 }
-                if (*count > limit - (typeof(limit))*pos)
-                        *count = limit - (typeof(limit))*pos;
+                iov_iter_truncate(from, limit - (unsigned long)pos);
         }
 
         /*
          * LFS rule
          */
-        if (unlikely(*pos + *count > MAX_NON_LFS &&
+        if (unlikely(pos + iov_iter_count(from) > MAX_NON_LFS &&
                                 !(file->f_flags & O_LARGEFILE))) {
-                if (*pos >= MAX_NON_LFS)
+                if (pos >= MAX_NON_LFS)
                         return -EFBIG;
-                if (*count > MAX_NON_LFS - (unsigned long)*pos)
-                        *count = MAX_NON_LFS - (unsigned long)*pos;
+                iov_iter_truncate(from, MAX_NON_LFS - (unsigned long)pos);
         }
 
         /*
@@ -2299,16 +2301,11 @@ inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count)
          * exceeded without writing data we send a signal and return EFBIG.
          * Linus frestrict idea will clean these up nicely..
          */
-        if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
-                if (*count || *pos > inode->i_sb->s_maxbytes) {
-                        return -EFBIG;
-                }
-                /* zero-length writes at ->s_maxbytes are OK */
-        }
+        if (unlikely(pos >= inode->i_sb->s_maxbytes))
+                return -EFBIG;
 
-        if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
-                *count = inode->i_sb->s_maxbytes - *pos;
-        return 0;
+        iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);
+        return iov_iter_count(from);
 }
 EXPORT_SYMBOL(generic_write_checks);
 
@@ -2618,14 +2615,11 @@ ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
         struct file *file = iocb->ki_filp;
         struct inode *inode = file->f_mapping->host;
         ssize_t ret;
-        size_t count = iov_iter_count(from);
 
         mutex_lock(&inode->i_mutex);
-        ret = generic_write_checks(file, &iocb->ki_pos, &count);
-        if (!ret && count) {
-                iov_iter_truncate(from, count);
+        ret = generic_write_checks(iocb, from);
+        if (ret > 0)
                 ret = __generic_file_write_iter(iocb, from);
-        }
         mutex_unlock(&inode->i_mutex);
 
         if (ret > 0) {