Reading Via The Page Cache

Entry function: do_generic_file_read, in mm/filemap.c:

• Get the address mapping of the file's inode.
• Translate the read position to a page index (each page contains 2^PAGE_CACHE_SHIFT bytes).
• Calculate read-ahead parameters (i.e. reading from a file at position X normally causes reading several more pages, assuming the application is likely to request those pages next).
• Make sure we're not reading past EOF.
• For each page in the range the user asked to read from:
  1. Look for the page in the page cache. If it is there, and
  2. If it's there, and is up-to-date:
     1. If we're not in 'non-blocking' mode (i.e. we're allowed to block), invoke read-ahead.
     2. Copy data from the page to the user's buffer.
  3. Otherwise, use the address mapping 'readpage' operation to read the page, and start over (unless we're in non-blocking mode).

Originally written by guy keren