[PATCH] don't apply file size rlimits to blockdevs

generic_file_write()'s rlimit checks are preventing writes to large
offsets into blockdevs:

# ulimit -f 10000
# dd if=/dev/zero of=/dev/sde5 bs=1k count=1 seek=1000000
zsh: file size limit exceeded

So don't apply that check if it's a blockdev.

The patch also caches the S_ISBLK result in a local.

diff --git a/mm/filemap.c b/mm/filemap.c
index cacecf650277deea1893d53b0221601044fd1e9b..2b993e3f842366b2dd3c94b81ac59259276f6e4a 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1530,6 +1530,7 @@ generic_file_write_nolock(struct file *file, const struct iovec *iov,
        size_t count;           /* after file limit checks */
        struct inode    *inode = mapping->host;
        unsigned long   limit = current->rlim[RLIMIT_FSIZE].rlim_cur;
+       const int       isblk = S_ISBLK(inode->i_mode);
        long            status = 0;
        loff_t          pos;
        struct page     *page;
@@ -1581,22 +1582,21 @@ generic_file_write_nolock(struct file *file, const struct iovec *iov,
 
        written = 0;
 
-       /* FIXME: this is for backwards compatibility with 2.4 */
-       if (!S_ISBLK(inode->i_mode) && file->f_flags & O_APPEND)
-               pos = inode->i_size;
+       if (!isblk) {
+               /* FIXME: this is for backwards compatibility with 2.4 */
+               if (file->f_flags & O_APPEND)
+                       pos = inode->i_size;
 
-       /*
-        * Check whether we've reached the file size limit.
-        */
-       if (unlikely(limit != RLIM_INFINITY)) {
-               if (pos >= limit) {
-                       send_sig(SIGXFSZ, current, 0);
-                       err = -EFBIG;
-                       goto out;
-               }
-               if (pos > 0xFFFFFFFFULL || count > limit - (u32)pos) {
-                       /* send_sig(SIGXFSZ, current, 0); */
-                       count = limit - (u32)pos;
+               if (limit != RLIM_INFINITY) {
+                       if (pos >= limit) {
+                               send_sig(SIGXFSZ, current, 0);
+                               err = -EFBIG;
+                               goto out;
+                       }
+                       if (pos > 0xFFFFFFFFULL || count > limit - (u32)pos) {
+                               /* send_sig(SIGXFSZ, current, 0); */
+                               count = limit - (u32)pos;
+                       }
                }
        }
 
@@ -1623,7 +1623,7 @@ generic_file_write_nolock(struct file *file, const struct iovec *iov,
         * exceeded without writing data we send a signal and return EFBIG.
         * Linus frestrict idea will clean these up nicely..
         */
-       if (likely(!S_ISBLK(inode->i_mode))) {
+       if (likely(!isblk)) {
                if (unlikely(pos >= inode->i_sb->s_maxbytes)) {
                        if (count || pos > inode->i_sb->s_maxbytes) {
                                send_sig(SIGXFSZ, current, 0);
@@ -1667,7 +1667,7 @@ generic_file_write_nolock(struct file *file, const struct iovec *iov,
                                        iov, pos, nr_segs);
                if (written > 0) {
                        loff_t end = pos + written;
-                       if (end > inode->i_size && !S_ISBLK(inode->i_mode)) {
+                       if (end > inode->i_size && !isblk) {
                                inode->i_size = end;
                                mark_inode_dirty(inode);
                        }