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Date: Mon, 5 Jan 2009 13:18:50 +0100
From: Jörn Engel <joern@...fs.org>
To: Phillip Lougher <phillip@...gher.demon.co.uk>
Cc: akpm@...ux-foundation.org, linux-embedded@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
tim.bird@...sony.com, sfr@...b.auug.org.au
Subject: Re: [PATCH V3 11/17] Squashfs: block operations
Again, none of my comments are criticism against merging squashfs. Code
improvements should continue independently.
On Mon, 5 January 2009 11:08:24 +0000, Phillip Lougher wrote:
> +/*
> + * Read and decompress a metadata block or datablock. Length is non-zero
> + * if a datablock is being read (the size is stored elsewhere in the
> + * filesystem), otherwise the length is obtained from the first two bytes of
> + * the metadata block. A bit in the length field indicates if the block
> + * is stored uncompressed in the filesystem (usually because compression
> + * generated a larger block - this does occasionally happen with zlib).
> + */
This is the core function of squashfs. As such, it could probably use
some kerneldoc that explains each parameter and the return value;
> +int squashfs_read_data(struct super_block *sb, void **buffer, u64 index,
> + int length, u64 *next_index, int srclength)
> +{
> + struct squashfs_sb_info *msblk = sb->s_fs_info;
> + struct buffer_head **bh;
> + int offset = index & ((1 << msblk->devblksize_log2) - 1);
> + u64 cur_index = index >> msblk->devblksize_log2;
> + int bytes, compressed, b = 0, k = 0, page = 0, avail;
> +
> +
> + bh = kcalloc((msblk->block_size >> msblk->devblksize_log2) + 1,
> + sizeof(*bh), GFP_KERNEL);
> + if (bh == NULL)
> + return -ENOMEM;
> +
> + if (length) {
> + /*
> + * Datablock.
> + */
> + bytes = -offset;
> + compressed = SQUASHFS_COMPRESSED_BLOCK(length);
> + length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
> + if (next_index)
> + *next_index = index + length;
> +
> + TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
> + index, compressed ? "" : "un", length, srclength);
> +
> + if (length < 0 || length > srclength ||
> + (index + length) > msblk->bytes_used)
> + goto read_failure;
> +
> + for (b = 0; bytes < length; b++, cur_index++) {
> + bh[b] = sb_getblk(sb, cur_index);
> + if (bh[b] == NULL)
> + goto block_release;
> + bytes += msblk->devblksize;
> + }
> + ll_rw_block(READ, b, bh);
> + } else {
> + /*
> + * Metadata block.
> + */
> + if ((index + 2) > msblk->bytes_used)
> + goto read_failure;
> +
> + bh[0] = get_block_length(sb, &cur_index, &offset, &length);
> + if (bh[0] == NULL)
> + goto read_failure;
> + b = 1;
> +
> + bytes = msblk->devblksize - offset;
> + compressed = SQUASHFS_COMPRESSED(length);
> + length = SQUASHFS_COMPRESSED_SIZE(length);
> + if (next_index)
> + *next_index = index + length + 2;
> +
> + TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
> + compressed ? "" : "un", length);
> +
> + if (length < 0 || length > srclength ||
> + (index + length) > msblk->bytes_used)
> + goto block_release;
> +
> + for (; bytes < length; b++) {
> + bh[b] = sb_getblk(sb, ++cur_index);
> + if (bh[b] == NULL)
> + goto block_release;
> + bytes += msblk->devblksize;
> + }
> + ll_rw_block(READ, b - 1, bh + 1);
> + }
> +
> + if (compressed) {
This looks like a prime candidate for a seperate function.
> + int zlib_err = 0, zlib_init = 0;
> +
> + /*
> + * Uncompress block.
> + */
> +
> + mutex_lock(&msblk->read_data_mutex);
> +
> + msblk->stream.avail_out = 0;
> + msblk->stream.avail_in = 0;
> +
> + bytes = length;
> + do {
> + if (msblk->stream.avail_in == 0 && k < b) {
> + avail = min(bytes, msblk->devblksize - offset);
> + bytes -= avail;
> + wait_on_buffer(bh[k]);
> + if (!buffer_uptodate(bh[k]))
> + goto release_mutex;
> +
> + if (avail == 0) {
> + offset = 0;
> + put_bh(bh[k++]);
> + continue;
> + }
> +
> + msblk->stream.next_in = bh[k]->b_data + offset;
> + msblk->stream.avail_in = avail;
> + offset = 0;
> + }
> +
> + if (msblk->stream.avail_out == 0) {
> + msblk->stream.next_out = buffer[page++];
> + msblk->stream.avail_out = PAGE_CACHE_SIZE;
> + }
> +
> + if (!zlib_init) {
Could be moved outside the main loop.
> + zlib_err = zlib_inflateInit(&msblk->stream);
> + if (zlib_err != Z_OK) {
> + ERROR("zlib_inflateInit returned"
> + " unexpected result 0x%x,"
> + " srclength %d\n", zlib_err,
> + srclength);
> + goto release_mutex;
> + }
> + zlib_init = 1;
> + }
> +
> + zlib_err = zlib_inflate(&msblk->stream, Z_NO_FLUSH);
> +
> + if (msblk->stream.avail_in == 0 && k < b)
> + put_bh(bh[k++]);
> + } while (zlib_err == Z_OK);
> +
> + if (zlib_err != Z_STREAM_END) {
> + ERROR("zlib_inflate returned unexpected result"
> + " 0x%x, srclength %d, avail_in %d,"
> + " avail_out %d\n", zlib_err, srclength,
> + msblk->stream.avail_in,
> + msblk->stream.avail_out);
> + goto release_mutex;
> + }
> +
> + zlib_err = zlib_inflateEnd(&msblk->stream);
> + if (zlib_err != Z_OK) {
> + ERROR("zlib_inflateEnd returned unexpected result 0x%x,"
> + " srclength %d\n", zlib_err, srclength);
> + goto release_mutex;
> + }
> + length = msblk->stream.total_out;
> + mutex_unlock(&msblk->read_data_mutex);
> + } else {
Another candidate for a seperate function. The complete condition could
look roughly like this:
if (compressed)
err = read_compressed_block(...);
else
err = read_uncompressed_block(...);
out:
kfree(bh);
if (err) {
ERROR("sb_bread failed reading block -1x%llx\n", cur_index);
return -EIO;
}
return length;
The only disadvantage I can see is the put_bh() loop in the error case
that would be duplicated in both read_*_block() functions.
> + /*
> + * Block is uncompressed.
> + */
> + int i, in, pg_offset = 0;
> +
> + for (i = 0; i < b; i++) {
> + wait_on_buffer(bh[i]);
> + if (!buffer_uptodate(bh[i]))
> + goto block_release;
> + }
> +
> + for (bytes = length; k < b; k++) {
> + in = min(bytes, msblk->devblksize - offset);
> + bytes -= in;
> + while (in) {
> + if (pg_offset == PAGE_CACHE_SIZE) {
> + page++;
> + pg_offset = 0;
> + }
> + avail = min_t(int, in, PAGE_CACHE_SIZE -
> + pg_offset);
> + memcpy(buffer[page] + pg_offset,
> + bh[k]->b_data + offset, avail);
> + in -= avail;
> + pg_offset += avail;
> + offset += avail;
> + }
> + offset = 0;
> + put_bh(bh[k]);
> + }
> + }
> +
> + kfree(bh);
> + return length;
> +
> +release_mutex:
> + mutex_unlock(&msblk->read_data_mutex);
> +
> +block_release:
> + for (; k < b; k++)
> + put_bh(bh[k]);
> +
> +read_failure:
> + ERROR("sb_bread failed reading block 0x%llx\n", cur_index);
> + kfree(bh);
> + return -EIO;
> +}
> --
> 1.5.6.3
>
> --
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Jörn
--
Optimizations always bust things, because all optimizations are, in
the long haul, a form of cheating, and cheaters eventually get caught.
-- Larry Wall
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