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fs: fat: refactor write interface for a file offset
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The current write implementation is quite simple: remove existing clusters
and then allocating new ones and filling them with data. This, inevitably,
enforces always writing from the beginning of a file.

As the first step to lift this restriction, fat_file_write() and
set_contents() are modified to accept an additional parameter, file offset
and further re-factored so that, in the next patch, all the necessary code
will be put into set_contents().

Signed-off-by: AKASHI Takahiro <[email protected]>
Signed-off-by: Alexander Graf <[email protected]>
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@agraf
AKASHI Takahiro authored and agraf committed Sep 23, 2018
1 parent 4ced203 commit 704df6a
Showing 1 changed file with 65 additions and 114 deletions.
179 changes: 65 additions & 114 deletions fs/fat/fat_write.c
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Original file line number Diff line number Diff line change
Expand Up @@ -528,36 +528,79 @@ static int clear_fatent(fsdata *mydata, __u32 entry)
return 0;
}

/*
* Set start cluster in directory entry
*/
static void set_start_cluster(const fsdata *mydata, dir_entry *dentptr,
__u32 start_cluster)
{
if (mydata->fatsize == 32)
dentptr->starthi =
cpu_to_le16((start_cluster & 0xffff0000) >> 16);
dentptr->start = cpu_to_le16(start_cluster & 0xffff);
}

/*
* Check whether adding a file makes the file system to
* exceed the size of the block device
* Return -1 when overflow occurs, otherwise return 0
*/
static int check_overflow(fsdata *mydata, __u32 clustnum, loff_t size)
{
__u32 startsect, sect_num, offset;

if (clustnum > 0)
startsect = clust_to_sect(mydata, clustnum);
else
startsect = mydata->rootdir_sect;

sect_num = div_u64_rem(size, mydata->sect_size, &offset);

if (offset != 0)
sect_num++;

if (startsect + sect_num > total_sector)
return -1;
return 0;
}

/*
* Write at most 'maxsize' bytes from 'buffer' into
* the file associated with 'dentptr'
* Update the number of bytes written in *gotsize and return 0
* or return -1 on fatal errors.
*/
static int
set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
loff_t maxsize, loff_t *gotsize)
set_contents(fsdata *mydata, dir_entry *dentptr, loff_t pos, __u8 *buffer,
loff_t maxsize, loff_t *gotsize)
{
loff_t filesize = FAT2CPU32(dentptr->size);
loff_t filesize;
unsigned int bytesperclust = mydata->clust_size * mydata->sect_size;
__u32 curclust = START(dentptr);
__u32 endclust = 0, newclust = 0;
loff_t actsize;

*gotsize = 0;
debug("Filesize: %llu bytes\n", filesize);

if (maxsize > 0 && filesize > maxsize)
filesize = maxsize;
filesize = maxsize;

debug("%llu bytes\n", filesize);

if (!curclust) {
if (filesize) {
debug("error: nonempty clusterless file!\n");
if (curclust) {
/*
* release already-allocated clusters anyway
*/
if (clear_fatent(mydata, curclust)) {
printf("Error: clearing FAT entries\n");
return -1;
}
return 0;
}

curclust = find_empty_cluster(mydata);
set_start_cluster(mydata, dentptr, curclust);

if (check_overflow(mydata, curclust, filesize)) {
printf("Error: no space left: %llu\n", filesize);
return -1;
}

actsize = bytesperclust;
Expand All @@ -568,6 +611,7 @@ set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
newclust = determine_fatent(mydata, endclust);

if ((newclust - 1) != endclust)
/* write to <curclust..endclust> */
goto getit;

if (CHECK_CLUST(newclust, mydata->fatsize)) {
Expand Down Expand Up @@ -614,18 +658,8 @@ set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
actsize = bytesperclust;
curclust = endclust = newclust;
} while (1);
}

/*
* Set start cluster in directory entry
*/
static void set_start_cluster(const fsdata *mydata, dir_entry *dentptr,
__u32 start_cluster)
{
if (mydata->fatsize == 32)
dentptr->starthi =
cpu_to_le16((start_cluster & 0xffff0000) >> 16);
dentptr->start = cpu_to_le16(start_cluster & 0xffff);
return 0;
}

/*
Expand All @@ -642,31 +676,6 @@ static void fill_dentry(fsdata *mydata, dir_entry *dentptr,
set_name(dentptr, filename);
}

/*
* Check whether adding a file makes the file system to
* exceed the size of the block device
* Return -1 when overflow occurs, otherwise return 0
*/
static int check_overflow(fsdata *mydata, __u32 clustnum, loff_t size)
{
__u32 startsect, sect_num, offset;

if (clustnum > 0) {
startsect = clust_to_sect(mydata, clustnum);
} else {
startsect = mydata->rootdir_sect;
}

sect_num = div_u64_rem(size, mydata->sect_size, &offset);

if (offset != 0)
sect_num++;

if (startsect + sect_num > total_sector)
return -1;
return 0;
}

/*
* Find a directory entry based on filename or start cluster number
* If the directory entry is not found,
Expand Down Expand Up @@ -784,18 +793,19 @@ static int normalize_longname(char *l_filename, const char *filename)
return 0;
}

static int do_fat_write(const char *filename, void *buffer, loff_t size,
loff_t *actwrite)
int file_fat_write_at(const char *filename, loff_t pos, void *buffer,
loff_t size, loff_t *actwrite)
{
dir_entry *retdent;
__u32 start_cluster;
fsdata datablock = { .fatbuf = NULL, };
fsdata *mydata = &datablock;
fat_itr *itr = NULL;
int ret = -1;
char *filename_copy, *parent, *basename;
char l_filename[VFAT_MAXLEN_BYTES];

debug("writing %s\n", filename);

filename_copy = strdup(filename);
if (!filename_copy)
return -ENOMEM;
Expand Down Expand Up @@ -839,47 +849,8 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
goto exit;
}

/* Update file size and start_cluster in a directory entry */
retdent->size = cpu_to_le32(size);
start_cluster = START(retdent);

if (start_cluster) {
if (size) {
ret = check_overflow(mydata, start_cluster,
size);
if (ret) {
printf("Error: %llu overflow\n", size);
ret = -ENOSPC;
goto exit;
}
}

ret = clear_fatent(mydata, start_cluster);
if (ret) {
printf("Error: clearing FAT entries\n");
ret = -EIO;
goto exit;
}

if (!size)
set_start_cluster(mydata, retdent, 0);
} else if (size) {
ret = start_cluster = find_empty_cluster(mydata);
if (ret < 0) {
printf("Error: finding empty cluster\n");
ret = -ENOSPC;
goto exit;
}

ret = check_overflow(mydata, start_cluster, size);
if (ret) {
printf("Error: %llu overflow\n", size);
ret = -ENOSPC;
goto exit;
}

set_start_cluster(mydata, retdent, start_cluster);
}
/* Update file size in a directory entry */
retdent->size = cpu_to_le32(pos + size);
} else {
/* Create a new file */

Expand Down Expand Up @@ -907,32 +878,13 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
goto exit;
}

if (size) {
ret = start_cluster = find_empty_cluster(mydata);
if (ret < 0) {
printf("Error: finding empty cluster\n");
ret = -ENOSPC;
goto exit;
}

ret = check_overflow(mydata, start_cluster, size);
if (ret) {
printf("Error: %llu overflow\n", size);
ret = -ENOSPC;
goto exit;
}
} else {
start_cluster = 0;
}

/* Set attribute as archive for regular file */
fill_dentry(itr->fsdata, itr->dent, filename,
start_cluster, size, 0x20);
fill_dentry(itr->fsdata, itr->dent, filename, 0, size, 0x20);

retdent = itr->dent;
}

ret = set_contents(mydata, retdent, buffer, size, actwrite);
ret = set_contents(mydata, retdent, pos, buffer, size, actwrite);
if (ret < 0) {
printf("Error: writing contents\n");
ret = -EIO;
Expand Down Expand Up @@ -971,6 +923,5 @@ int file_fat_write(const char *filename, void *buffer, loff_t offset,
return -EINVAL;
}

printf("writing %s\n", filename);
return do_fat_write(filename, buffer, maxsize, actwrite);
return file_fat_write_at(filename, offset, buffer, maxsize, actwrite);
}

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