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Revises the comments using fallocate().

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This commit is contained in:
Andrea Mazzoleni 2012-01-21 21:52:37 +01:00
parent c4263a4193
commit 13596d07ea
1 changed files with 9 additions and 7 deletions
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16
parity.c
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@ -75,19 +75,21 @@ int parity_create(struct snapraid_parity* parity, const char* path, data_off_t s
if (parity->st.st_size < size) {
#if HAVE_FALLOCATE
/* allocate real space using the specific Linux fallocate() operation. */
/* If the underline filesystem doesn't support it, it's going to fail with the ENOSYS error. */
/* Note that posix_fallocate() doesn't fail in such case, and fallbacks to write the whole file. */
/* If the underline filesystem doesn't support it, this operation fails, */
/* instead posix_fallocate() fallbacks to write the whole file. */
ret = fallocate(parity->f, 0, 0, size);
/* fallocate() returns the error number, and it doesn't set errno, just like posix_fallocate() */
/* It's not clear if this is correct or a bug, as the official manpage says otherwise */
/* http://www.kernel.org/doc/man-pages/online/pages/man2/fallocate.2.html */
if (ret > 0) { /* if an error is returned, move it to errno */
/* fallocate() returns the error number as positive integer, */
/* and in this case it doesn't set errno, just like posix_fallocate() */
/* Checking the glibc code (2.11.1 and 2.14.1) it seems that ENOSYS */
/* may be returned in errno, so we support both the return way */
if (ret > 0) { /* if a positive error is returned, convert it to errno */
errno = ret;
ret = -1;
}
/* if the operation is not supported, like in ext3 */
/* we get EOPNOTSUPP if the operation is not supported, like in ext3/ext2 */
/* or ENOSYS with kernel before 2.6.23 */
if (errno == EOPNOTSUPP || errno == ENOSYS) {
/* fallback using ftruncate() */
ret = ftruncate(parity->f, size);