libext2fs: refactor Direct I/O alignment requirement calculations

Create a new function, ext2fs_get_dio_alignment(), which returns the
alignment requirements for direct I/O.  This way we can factor out the
code from MMP and the Unix I/O manager.  The two modules weren't
consistently calculating the alignment factors, and in particular MMP
would sometimes use a larger alignment factor than was strictly
necessary.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index fda6ade..9a0e736 100644 (file)
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -1213,6 +1213,7 @@ extern errcode_t ext2fs_get_device_size2(const char *file, int blocksize,
                                        blk64_t *retblocks);
 
 /* getsectsize.c */
+extern int ext2fs_get_dio_alignment(int fd);
 errcode_t ext2fs_get_device_sectsize(const char *file, int *sectsize);
 errcode_t ext2fs_get_device_phys_sectsize(const char *file, int *sectsize);
 

diff --git a/lib/ext2fs/getsectsize.c b/lib/ext2fs/getsectsize.c
index 30faecc..9c3f4a2 100644 (file)
--- a/lib/ext2fs/getsectsize.c
+++ b/lib/ext2fs/getsectsize.c
@@ -62,6 +62,32 @@ errcode_t ext2fs_get_device_sectsize(const char *file, int *sectsize)
 }
 
 /*
+ * Return desired alignment for direct I/O
+ */
+int ext2fs_get_dio_alignment(int fd)
+{
+       int align = 0;
+
+#ifdef BLKSSZGET
+       if (ioctl(fd, BLKSSZGET, &align) < 0)
+               align = 0;
+#endif
+
+#ifdef _SC_PAGESIZE
+       if (align <= 0)
+               align = sysconf(_SC_PAGESIZE);
+#endif
+#ifdef HAVE_GETPAGESIZE
+       if (align <= 0)
+               align = getpagesize();
+#endif
+       if (align <= 0)
+               align = 4096;
+
+       return align;
+}
+
+/*
  * Returns the physical sector size of a device
  */
 errcode_t ext2fs_get_device_phys_sectsize(const char *file, int *sectsize)

diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
index 49a11da..bb3772d 100644 (file)
--- a/lib/ext2fs/mmp.c
+++ b/lib/ext2fs/mmp.c
@@ -27,20 +27,6 @@
 #include "ext2fs/ext2_fs.h"
 #include "ext2fs/ext2fs.h"
 
-static int mmp_pagesize(void)
-{
-#ifdef _SC_PAGESIZE
-       int sysval = sysconf(_SC_PAGESIZE);
-       if (sysval > 0)
-               return sysval;
-#endif /* _SC_PAGESIZE */
-#ifdef HAVE_GETPAGESIZE
-       return getpagesize();
-#else
-       return 4096;
-#endif
-}
-
 #ifndef O_DIRECT
 #define O_DIRECT 0
 #endif
@@ -54,20 +40,6 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
            (mmp_blk >= fs->super->s_blocks_count))
                return EXT2_ET_MMP_BAD_BLOCK;
 
-       if (fs->mmp_cmp == NULL) {
-               /* O_DIRECT in linux 2.4: page aligned
-                * O_DIRECT in linux 2.6: sector aligned
-                * A filesystem cannot be created with blocksize < sector size,
-                * or with blocksize > page_size. */
-               int bufsize = fs->blocksize;
-
-               if (bufsize < mmp_pagesize())
-                       bufsize = mmp_pagesize();
-               retval = ext2fs_get_memalign(bufsize, bufsize, &fs->mmp_cmp);
-               if (retval)
-                       return retval;
-       }
-
        /* ext2fs_open() reserves fd0,1,2 to avoid stdio collision, so checking
         * mmp_fd <= 0 is OK to validate that the fd is valid.  This opens its
         * own fd to read the MMP block to ensure that it is using O_DIRECT,
@@ -81,6 +53,15 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
                }
        }
 
+       if (fs->mmp_cmp == NULL) {
+               int align = ext2fs_get_dio_alignment(fs->mmp_fd);
+
+               retval = ext2fs_get_memalign(fs->blocksize, align,
+                                            &fs->mmp_cmp);
+               if (retval)
+                       return retval;
+       }
+
        if (ext2fs_llseek(fs->mmp_fd, mmp_blk * fs->blocksize, SEEK_SET) !=
            mmp_blk * fs->blocksize) {
                retval = EXT2_ET_LLSEEK_FAILED;

diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 3269392..8319eba 100644 (file)
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -58,10 +58,6 @@
 #define BLKROGET   _IO(0x12, 94) /* Get read-only status (0 = read_write).  */
 #endif
 
-#if defined(__linux__) && defined(_IO) && !defined(BLKSSZGET)
-#define BLKSSZGET  _IO(0x12,104)/* get block device sector size */
-#endif
-
 #undef ALIGN_DEBUG
 
 #include "ext2_fs.h"
@@ -485,11 +481,15 @@ static errcode_t unix_open(const char *name, int flags, io_channel *channel)
        if (flags & IO_FLAG_EXCLUSIVE)
                open_flags |= O_EXCL;
 #if defined(O_DIRECT)
-       if (flags & IO_FLAG_DIRECT_IO)
+       if (flags & IO_FLAG_DIRECT_IO) {
                open_flags |= O_DIRECT;
+               io->align = ext2fs_get_dio_alignment(data->dev);
+       }
 #elif defined(F_NOCACHE)
-       if (flags & IO_FLAG_DIRECT_IO)
+       if (flags & IO_FLAG_DIRECT_IO) {
                f_nocache = F_NOCACHE;
+               io->align = 4096;
+       }
 #endif
        data->flags = flags;
 
@@ -519,13 +519,6 @@ static errcode_t unix_open(const char *name, int flags, io_channel *channel)
                        io->flags |= CHANNEL_FLAGS_DISCARD_ZEROES;
        }
 
-#ifdef BLKSSZGET
-       if (flags & IO_FLAG_DIRECT_IO) {
-               if (ioctl(data->dev, BLKSSZGET, &io->align) != 0)
-                       io->align = io->block_size;
-       }
-#endif
-
 #ifdef BLKDISCARDZEROES
        ioctl(data->dev, BLKDISCARDZEROES, &zeroes);
        if (zeroes)
@@ -537,7 +530,8 @@ static errcode_t unix_open(const char *name, int flags, io_channel *channel)
         * Some operating systems require that the buffers be aligned,
         * regardless of O_DIRECT
         */
-       io->align = 512;
+       if (!io->align)
+               io->align = 512;
 #endif