1 files changed, 90 insertions, 61 deletions

diff --git a/fs/seq_file.c b/fs/seq_file.c
index b569ff1c4dc8..a1a4cfe19210 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -48,12 +48,78 @@ int seq_open(struct file *file, const struct seq_operations *op)
          */
         file->f_version = 0;
 
-        /* SEQ files support lseek, but not pread/pwrite */
-        file->f_mode &= ~(FMODE_PREAD | FMODE_PWRITE);
+        /*
+         * seq_files support lseek() and pread().  They do not implement
+         * write() at all, but we clear FMODE_PWRITE here for historical
+         * reasons.
+         *
+         * If a client of seq_files a) implements file.write() and b) wishes to
+         * support pwrite() then that client will need to implement its own
+         * file.open() which calls seq_open() and then sets FMODE_PWRITE.
+         */
+        file->f_mode &= ~FMODE_PWRITE;
         return 0;
 }
 EXPORT_SYMBOL(seq_open);
 
+static int traverse(struct seq_file *m, loff_t offset)
+{
+        loff_t pos = 0, index;
+        int error = 0;
+        void *p;
+
+        m->version = 0;
+        index = 0;
+        m->count = m->from = 0;
+        if (!offset) {
+                m->index = index;
+                return 0;
+        }
+        if (!m->buf) {
+                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
+                if (!m->buf)
+                        return -ENOMEM;
+        }
+        p = m->op->start(m, &index);
+        while (p) {
+                error = PTR_ERR(p);
+                if (IS_ERR(p))
+                        break;
+                error = m->op->show(m, p);
+                if (error < 0)
+                        break;
+                if (unlikely(error)) {
+                        error = 0;
+                        m->count = 0;
+                }
+                if (m->count == m->size)
+                        goto Eoverflow;
+                if (pos + m->count > offset) {
+                        m->from = offset - pos;
+                        m->count -= m->from;
+                        m->index = index;
+                        break;
+                }
+                pos += m->count;
+                m->count = 0;
+                if (pos == offset) {
+                        index++;
+                        m->index = index;
+                        break;
+                }
+                p = m->op->next(m, p, &index);
+        }
+        m->op->stop(m, p);
+        m->index = index;
+        return error;
+
+Eoverflow:
+        m->op->stop(m, p);
+        kfree(m->buf);
+        m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
+        return !m->buf ? -ENOMEM : -EAGAIN;
+}
+
 /**
  *      seq_read -      ->read() method for sequential files.
  *      @file: the file to read from
@@ -73,6 +139,22 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
         int err = 0;
 
         mutex_lock(&m->lock);
+
+        /* Don't assume *ppos is where we left it */
+        if (unlikely(*ppos != m->read_pos)) {
+                m->read_pos = *ppos;
+                while ((err = traverse(m, *ppos)) == -EAGAIN)
+                        ;
+                if (err) {
+                        /* With prejudice... */
+                        m->read_pos = 0;
+                        m->version = 0;
+                        m->index = 0;
+                        m->count = 0;
+                        goto Done;
+                }
+        }
+
         /*
          * seq_file->op->..m_start/m_stop/m_next may do special actions
          * or optimisations based on the file->f_version, so we want to
@@ -172,8 +254,10 @@ Fill:
 Done:
         if (!copied)
                 copied = err;
-        else
+        else {
                 *ppos += copied;
+                m->read_pos += copied;
+        }
         file->f_version = m->version;
         mutex_unlock(&m->lock);
         return copied;
@@ -186,63 +270,6 @@ Efault:
 }
 EXPORT_SYMBOL(seq_read);
 
-static int traverse(struct seq_file *m, loff_t offset)
-{
-        loff_t pos = 0, index;
-        int error = 0;
-        void *p;
-
-        m->version = 0;
-        index = 0;
-        m->count = m->from = 0;
-        if (!offset) {
-                m->index = index;
-                return 0;
-        }
-        if (!m->buf) {
-                m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);
-                if (!m->buf)
-                        return -ENOMEM;
-        }
-        p = m->op->start(m, &index);
-        while (p) {
-                error = PTR_ERR(p);
-                if (IS_ERR(p))
-                        break;
-                error = m->op->show(m, p);
-                if (error < 0)
-                        break;
-                if (unlikely(error)) {
-                        error = 0;
-                        m->count = 0;
-                }
-                if (m->count == m->size)
-                        goto Eoverflow;
-                if (pos + m->count > offset) {
-                        m->from = offset - pos;
-                        m->count -= m->from;
-                        m->index = index;
-                        break;
-                }
-                pos += m->count;
-                m->count = 0;
-                if (pos == offset) {
-                        index++;
-                        m->index = index;
-                        break;
-                }
-                p = m->op->next(m, p, &index);
-        }
-        m->op->stop(m, p);
-        return error;
-
-Eoverflow:
-        m->op->stop(m, p);
-        kfree(m->buf);
-        m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
-        return !m->buf ? -ENOMEM : -EAGAIN;
-}
-
 /**
  *      seq_lseek -     ->llseek() method for sequential files.
  *      @file: the file in question
@@ -265,16 +292,18 @@ loff_t seq_lseek(struct file *file, loff_t offset, int origin)
                         if (offset < 0)
                                 break;
                         retval = offset;
-                        if (offset != file->f_pos) {
+                        if (offset != m->read_pos) {
                                 while ((retval=traverse(m, offset)) == -EAGAIN)
                                         ;
                                 if (retval) {
                                         /* with extreme prejudice... */
                                         file->f_pos = 0;
+                                        m->read_pos = 0;
                                         m->version = 0;
                                         m->index = 0;
                                         m->count = 0;
                                 } else {
+                                        m->read_pos = offset;
                                         retval = file->f_pos = offset;
                                 }
                         }