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The problem that has been addressed is that of synchronising updates of the file size with writes that extend a file. Without the fix the update of a file's size, as a result of a write beyond eof, is independent of when the cached data is flushed to disk. Often the file size update would be written to the filesystem log before the data is flushed to disk. When a system crashes between these two events and the filesystem log is replayed on mount the file's size will be set but since the contents never made it to disk the file is full of holes. If some of the cached data was flushed to disk then it may just be a section of the file at the end that has holes. There are existing fixes to help alleviate this problem, particularly in the case where a file has been truncated, that force cached data to be flushed to disk when the file is closed. If the system crashes while the file(s) are still open then this flushing will never occur. The fix that we have implemented is to introduce a second file size, called the in-memory file size, that represents the current file size as viewed by the user. The existing file size, called the on-disk file size, is the one that get's written to the filesystem log and we only update it when it is safe to do so. When we write to a file beyond eof we only update the in- memory file size in the write operation. Later when the I/O operation, that flushes the cached data to disk completes, an I/O completion routine will update the on-disk file size. The on-disk file size will be updated to the maximum offset of the I/O or to the value of the in-memory file size if the I/O includes eof. SGI-PV: 958522 SGI-Modid: xfs-linux-melb:xfs-kern:28322a Signed-off-by: Lachlan McIlroy <lachlan@sgi.com> Signed-off-by: David Chinner <dgc@sgi.com> Signed-off-by: Tim Shimmin <tes@sgi.com>
91 lines
3.5 KiB
C
91 lines
3.5 KiB
C
/*
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* Copyright (c) 2003-2005 Silicon Graphics, Inc.
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* All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it would be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef __XFS_IOMAP_H__
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#define __XFS_IOMAP_H__
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#define IOMAP_DADDR_NULL ((xfs_daddr_t) (-1LL))
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typedef enum { /* iomap_flags values */
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IOMAP_READ = 0, /* mapping for a read */
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IOMAP_EOF = 0x01, /* mapping contains EOF */
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IOMAP_HOLE = 0x02, /* mapping covers a hole */
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IOMAP_DELAY = 0x04, /* mapping covers delalloc region */
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IOMAP_REALTIME = 0x10, /* mapping on the realtime device */
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IOMAP_UNWRITTEN = 0x20, /* mapping covers allocated */
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/* but uninitialized file data */
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IOMAP_NEW = 0x40 /* just allocate */
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} iomap_flags_t;
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typedef enum {
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/* base extent manipulation calls */
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BMAPI_READ = (1 << 0), /* read extents */
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BMAPI_WRITE = (1 << 1), /* create extents */
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BMAPI_ALLOCATE = (1 << 2), /* delayed allocate to real extents */
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BMAPI_UNWRITTEN = (1 << 3), /* unwritten extents to real extents */
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/* modifiers */
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BMAPI_IGNSTATE = (1 << 4), /* ignore unwritten state on read */
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BMAPI_DIRECT = (1 << 5), /* direct instead of buffered write */
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BMAPI_MMAP = (1 << 6), /* allocate for mmap write */
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BMAPI_SYNC = (1 << 7), /* sync write to flush delalloc space */
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BMAPI_TRYLOCK = (1 << 8), /* non-blocking request */
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BMAPI_DEVICE = (1 << 9), /* we only want to know the device */
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} bmapi_flags_t;
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/*
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* xfs_iomap_t: File system I/O map
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*
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* The iomap_bn field is expressed in 512-byte blocks, and is where the
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* mapping starts on disk.
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*
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* The iomap_offset, iomap_bsize and iomap_delta fields are in bytes.
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* iomap_offset is the offset of the mapping in the file itself.
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* iomap_bsize is the size of the mapping, iomap_delta is the
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* desired data's offset into the mapping, given the offset supplied
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* to the file I/O map routine.
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*
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* When a request is made to read beyond the logical end of the object,
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* iomap_size may be set to 0, but iomap_offset and iomap_length should be set
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* to the actual amount of underlying storage that has been allocated, if any.
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*/
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typedef struct xfs_iomap {
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xfs_daddr_t iomap_bn; /* first 512b blk of mapping */
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xfs_buftarg_t *iomap_target;
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xfs_off_t iomap_offset; /* offset of mapping, bytes */
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xfs_off_t iomap_bsize; /* size of mapping, bytes */
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xfs_off_t iomap_delta; /* offset into mapping, bytes */
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iomap_flags_t iomap_flags;
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} xfs_iomap_t;
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struct xfs_iocore;
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struct xfs_inode;
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struct xfs_bmbt_irec;
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extern int xfs_iomap(struct xfs_iocore *, xfs_off_t, ssize_t, int,
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struct xfs_iomap *, int *);
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extern int xfs_iomap_write_direct(struct xfs_inode *, xfs_off_t, size_t,
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int, struct xfs_bmbt_irec *, int *, int);
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extern int xfs_iomap_write_delay(struct xfs_inode *, xfs_off_t, size_t, int,
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struct xfs_bmbt_irec *, int *);
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extern int xfs_iomap_write_allocate(struct xfs_inode *, xfs_off_t, size_t,
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struct xfs_bmbt_irec *, int *);
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extern int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, size_t);
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#endif /* __XFS_IOMAP_H__*/
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