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Subject: Re: [PATCH v2 05/13] exfat: add file operations
To:     Namjae Jeon <namjae.jeon@samsung.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc:     gregkh@linuxfoundation.org, valdis.kletnieks@vt.edu, hch@lst.de,
        linkinjeon@gmail.com, Markus.Elfring@web.de, sj1557.seo@samsung.com
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 <20191119071107.1947-6-namjae.jeon@samsung.com>
From:   Nikolay Borisov <nborisov@suse.com>
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Message-ID: <398eeca9-e59f-385b-791d-561e56567026@suse.com>
Date:   Wed, 20 Nov 2019 11:14:20 +0200
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On 19.11.19 г. 9:10 ч., Namjae Jeon wrote:
> This adds the implementation of file operations for exfat.
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
> ---
>  fs/exfat/file.c | 346 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 346 insertions(+)
>  create mode 100644 fs/exfat/file.c
> 
> diff --git a/fs/exfat/file.c b/fs/exfat/file.c
> new file mode 100644
> index 000000000000..5afd65a36eb5
> --- /dev/null
> +++ b/fs/exfat/file.c
> @@ -0,0 +1,346 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2012-2013 Samsung Electronics Co., Ltd.
> + */
> +
> +#include <linux/slab.h>
> +#include <linux/cred.h>
> +#include <linux/buffer_head.h>
> +
> +#include "exfat_raw.h"
> +#include "exfat_fs.h"
> +

<snip>

> +
> +static int exfat_allow_set_time(struct exfat_sb_info *sbi, struct inode *inode)
> +{
> +	mode_t allow_utime = sbi->options.allow_utime;
> +
> +	if (!uid_eq(current_fsuid(), inode->i_uid)) {
> +		if (in_group_p(inode->i_gid))
> +			allow_utime >>= 3;
> +		if (allow_utime & MAY_WRITE)
> +			return 1;
> +	}
> +
> +	/* use a default check */
> +	return 0;

this function can be made to return bool.

> +}
> +

<snip>

> +/* resize the file length */
> +int __exfat_truncate(struct inode *inode, loff_t new_size)
> +{
> +	unsigned int num_clusters_new, num_clusters_phys;
> +	unsigned int last_clu = FREE_CLUSTER;
> +	struct exfat_chain clu;
> +	struct exfat_timestamp tm;
> +	struct exfat_dentry *ep, *ep2;
> +	struct super_block *sb = inode->i_sb;
> +	struct exfat_sb_info *sbi = EXFAT_SB(sb);
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +	struct exfat_entry_set_cache *es = NULL;
> +	int evict = (ei->dir.dir == DIR_DELETED) ? 1 : 0;
> +
> +	/* check if the given file ID is opened */
> +	if (ei->type != TYPE_FILE && ei->type != TYPE_DIR)
> +		return -EPERM;
> +
> +	exfat_set_vol_flags(sb, VOL_DIRTY);
> +
> +	num_clusters_new = EXFAT_B_TO_CLU_ROUND_UP(i_size_read(inode), sbi);
> +	num_clusters_phys =
> +		EXFAT_B_TO_CLU_ROUND_UP(EXFAT_I(inode)->i_size_ondisk, sbi);
> +
> +	exfat_chain_set(&clu, ei->start_clu, num_clusters_phys, ei->flags);
> +
> +	if (new_size > 0) {
> +		/*
> +		 * Truncate FAT chain num_clusters after the first cluster
> +		 * num_clusters = min(new, phys);
> +		 */
> +		unsigned int num_clusters =
> +			min(num_clusters_new, num_clusters_phys);
> +
> +		/*
> +		 * Follow FAT chain
> +		 * (defensive coding - works fine even with corrupted FAT table
> +		 */
> +		if (clu.flags == 0x03) {

That 0x03 is magic constant, better define actual flags and check
clu.flag == (FLAG1|FLAG2)

> +			clu.dir += num_clusters;
> +			clu.size -= num_clusters;
> +		} else {
> +			while (num_clusters > 0) {
> +				last_clu = clu.dir;
> +				if (exfat_get_next_cluster(sb, &(clu.dir)))
> +					return -EIO;
> +
> +				num_clusters--;
> +				clu.size--;
> +			}
> +		}
> +	} else {
> +		ei->flags = 0x03;

again, magic constant.
> +		ei->start_clu = EOF_CLUSTER;
> +	}
> +
> +	i_size_write(inode, new_size);
> +
> +	if (ei->type == TYPE_FILE)
> +		ei->attr |= ATTR_ARCHIVE;

<snip>